Water - Simple English Wikipedia, the free encyclopedia

Water - Simple English Wikipedia, the free encyclopedia
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From Simple English Wikipedia, the free encyclopedia
For water in its
solid
state, see
Ice
For water in its
gas
state, see
Water vapor
Water (
Ball-and-stick model of a water molecule
Space filling model of a water molecule
Names
IUPAC name
water, oxidane
Other names
Hydrogen hydroxide (HH or HOH), hydrogen oxide, dihydrogen monoxide (DHMO) (systematic name
), hydrogen monoxide, dihydrogen oxide, hydric acid, hydrohydroxic acid, hydroxic acid, hydrol,
μ-oxido dihydrogen, κ
-hydroxyl hydrogen(0)
Identifiers
CAS Number
7732-18-5
3D model (
JSmol
Interactive image
Beilstein Reference
3587155
ChEBI
CHEBI:15377
ChEMBL
ChEMBL1098659
ChemSpider
937
ECHA InfoCard
100.028.902
Gmelin Reference
117
PubChem
CID
962
RTECS number
ZC0110000
UNII
059QF0KO0R
CompTox Dashboard
EPA
DTXSID6026296
SMILES
Properties
Chemical formula
Molar mass
18.01528(33) g/mol
Appearance
White crystal-like solid, almost colorless liquid with a hint of blue, colorless gas
Odor
None
Density
Liquid:
0.9998396
g/mL at 0
°C
0.9970474
g/mL at 25
°C
0.961893
g/mL at 95
°C
Solid:
0.9167
g/ml at 0
°C
Melting point
0.00
°C (32.00
°F; 273.15
K)
Boiling point
99.98
°C (211.96
°F; 373.13
K)
Solubility in water
N/A
Solubility
Poorly soluble in
haloalkanes
aliphatic
and
aromatic
hydrocarbons,
ethers
Improved solubility in
carboxylates
alcohols
ketones
amines
. Miscible with
methanol
ethanol
propanol
isopropanol
acetone
glycerol
1,4-dioxane
tetrahydrofuran
sulfolane
acetaldehyde
dimethylformamide
dimethoxyethane
dimethyl sulfoxide
acetonitrile
. Partially miscible with
diethyl ether
methyl ethyl ketone
dichloromethane
ethyl acetate
bromine
Vapor pressure
3.1690 kilopascals or 0.031276
atm
Acidity
(p
13.995
Basicity
(p
13.995
Conjugate acid
Hydronium
Conjugate base
Hydroxide
Thermal conductivity
0.6065 W/(m·K)
12
Refractive index
1.3330 (20
°C)
13
Viscosity
0.890
cP
14
Structure
Crystal structure
Hexagonal
Point group
2v
Molecular shape
Bent
Dipole moment
1.8546
15
Thermochemistry
Std enthalpy of
formation
298
−285.83 ± 0.04
kJ/mol
16
Standard molar
entropy
298
69.95 ± 0.03
J/(mol·K)
16
Specific heat capacity
75.385 ± 0.05
J/(mol·K)
16
Hazards
Occupational safety and health
(OHS/OSH):
Main hazards
Drowning
Avalanche
(as snow)
Water intoxication
(see also
Dihydrogen monoxide parody
NFPA 704
(fire
diamond)
Flash point
Non-flammable
Related compounds
Other
cations
Hydrogen sulfide
Hydrogen selenide
Hydrogen telluride
Hydrogen polonide
Hydrogen peroxide
Related
solvents
Acetone
Methanol
Except where otherwise noted, data are given for materials in their
standard state
(at 25
°C [77
°F], 100
kPa).
verify
what is
?)
Infobox
references
Water in three
states
liquid
(including the clouds, which are
aerosols
),
solid
ice
) and
gas
water vapour
Water
) is a simple
chemical compound
made of two
hydrogen atoms
and one
oxygen atom
. It is clear, has no
taste
or
smell
, and is almost colorless. All
living things
need water to survive.
17
Water molecules stick together because of
hydrogen bonds
. These bonds give water special properties. For example, water has high
surface tension
, and can dissolve many substances. Water exists in three forms on
Earth
solid
(ice),
liquid
(water), and
gas
(water vapor). The word "water" comes from the Old English word wæter.
18
About 71% of Earth’s surface is covered by water. Most of this water (about 97%) is in the
oceans
. This water is
salt water
, which we cannot drink or use for farming. Only 3% of Earth’s water is
fresh water
, and even that is not easy to get. 69% of all fresh water is frozen in
glaciers
and
ice caps
. 30% is stored underground in
aquifers
. Less than 1% is in
lakes
rivers
, and
swamps
. If you look at all the water on Earth, only about 1% can be used by us. And most of that water is found underground.
19
20
Water is always moving in a cycle. This is called the water cycle. It includes:
21
22
Evaporation
(water turns into vapor),
Transpiration
(plants release water vapor),
Condensation
(vapor forms clouds),
Precipitation
(rain or snow falls),
Runoff
(water returns to oceans and lakes).
Water has many unique abilities.
23
One is that it expands when it freezes. This makes ice less dense than liquid water, so ice floats.
24
25
Water also has a high
specific heat capacity
. It can absorb or lose a lot of heat without changing temperature much.
26
This helps keep Earth's
climate
stable.
27
Water’s
surface tension
lets it form
droplets
. It also lets small insects walk on water.
28
Water is an excellent
solvent
. It can dissolve more substances than any other liquid. This is why it is called the "universal solvent." However, it cannot dissolve
oily
or nonpolar substances well.
29
30
31
32
These special abilities come from water's
polar nature
and the hydrogen bonds between them.
33
Water is important for all living things. Every kind of life we know needs water to survive. This includes tiny living things like
bacteria
archaea
, and
protists
, and bigger ones like
fungi
plants
and
animals
34
The human body is about 50-60% water.
35
Water helps move
nutrients
, gases, and
waste
inside the body. Inside
cells
, water is where most
chemical reactions
happen. It also helps cells keep their shape. Water is needed for
digestion
in animals, and
photosynthesis
in plants.
36
It also helps control
body temperature
. Without water, life could not exist. That is why water is one of the most important substances for all living things.
37
Water is also very important to the
world economy
. About 70% of the fresh water people use goes to
farming
38
Water is used to grow
crops
and raise
animals
39
Fish
from oceans, lakes, and rivers are an important source of food.
40
Many products, like
crude oil
and other goods, are moved around the world by
ships
through oceans,
rivers
, and
canals
41
Water is also used to heat and cool buildings and machines. Because it can dissolve many substances, it is very useful in
factories
cooking
, and
cleaning
. Water can also be used to make
electricity
, using
hydroelectric plants
42
It is also used for fun activities like
swimming
boating
fishing
diving
ice skating
snowboarding
, and
skiing
43
Many
civilizations
in history began near rivers or other places where they could get water easily. For example,
Mesopotamia
began between the
Tigris
and
Euphrates
rivers.
44
Ancient Egypt
depended on the
Nile
45
The
Indus Valley civilization
started near the
Indus River
46
Ancient Rome
was built near the
Tiber River
47
Even today, many big
cities
like
London
New York
, and
Shanghai
grew near water.
48
Being close to rivers or oceans made it easier to
trade
and
travel
49
50
Islands
with good
harbors
, like
Singapore
, also became rich and powerful because ships could stop there easily.
51
In dry places like
North Africa
and the
Middle East
, clean water has always been important. Having water often made the difference between a small village and a strong civilization.
52
Water is not just found on Earth. Scientists have discovered water in many places in
space
. Ice has been found on
Mars
, and even on
the Moon
53
Some
moons
in our
solar system
, like
Europa
and
Ganymede
(around
Jupiter
), and
Enceladus
(around
Saturn
) may have liquid water under their icy surfaces.
54
55
56
57
Water vapor has also been found in the
atmosphere
of some
exoplanets
. These are
planets
that
orbit
stars
far away from our solar system.
58
59
Water has even been found in clouds of gas and dust in space where new stars are being born.
60
History
change
change source
In the Universe
change
change source
Artist's impression of the
debris ring
around HD 181327
Shortly after the
Big Bang
, around 13.8 billion years ago, the
universe
was a hot, dense soup of
particles
. After 380 000 years, the universe expanded and cooled down enough for the first
atomic nuclei
to form in a process known as
Big Bang nucleosynthesis
. This produced mostly hydrogen, with smaller amounts of
helium
and trace amounts of
lithium
and
beryllium
Oxygen
and heavier elements did not yet exist, meaning water could not yet form.
61
62
Hundreds of millions of years later, the first
stars
were made from clouds of hydrogen and helium. Inside these stars,
nuclear fusion
began to produce heavier elements. In massive stars, fusion of lighter elements created heavier elements like carbon, nitrogen, and finally oxygen (a key ingredient for water). When these massive stars reached the end of their lives, they exploded as supernovae. This scattered those elements, including oxygen, into the
interstellar medium
63
Now that hydrogen and oxygen existed in the universe, they began to react and form water (H₂O). This happened mainly in
molecular clouds
. Here, water could form in two ways. On dust grains, hydrogen and oxygen atoms stuck to the surface can react to form
water ice
. In hot places inside the molecular cloud like around
young stars
, hydrogen and oxygen gas could react to form
water vapor
64
65
As molecular clouds collapsed to form new stars,
protoplanetary disks
(flat disks of gas and dust moving around the star) formed around these young stars. Water in these disks could be found as water vapor or ice. This depended on how close or far away the water was from the star. The "
snow line
" is a place far away from the star where it is cold enough for water to freeze and turn into ice. Inside this line, water stays as a gas, but beyond it, water becomes ice. This ice allowed particles to clump together and form planets. Water got trapped in icy
planetesimals
comets
, and
asteroids
. In the inner parts of
star systems
, it was usually too warm for ice, so most water there was in the form of vapor. Some water may have arrived later when comets or water-rich asteroids from the colder outer regions crashed into these inner planets, bringing ice that had formed far from the star.
66
67
On some
planets
and
moons
, the conditions were just right for water to exist as a liquid, solid (ice), or gas (vapor).
Earth
is the best and only example we know of. Because it is the right distance from the
Sun
and has a protective
atmosphere
, it has had oceans of liquid water for billions of years. Other places, like the moons
Europa
Enceladus
, and
Ganymede
, have oceans hidden under thick layers of ice.
Mars
has signs that it once had
rivers
and
lakes
long ago. Comets and asteroids still hold water from the early days of the
solar system
68
Today, water continues to be everywhere but mostly frozen or in vapor form. It found in molecular clouds, where stars and planets are still being made. It can also be found in
interstellar space
as ice on
dust
grains. It has also been found in the atmospheres of exoplanets. At the center of
galaxies
, massive amounts of water, billions of times the amount on Earth has been found around
black holes
. But, liquid water remains extremely rare, because it requires a very narrow set of conditions. Earth is unique because it contains liquid water on its surface.
69
On Earth
change
change source
Main article:
Origin of water on Earth
Water, oceans, lakes, and rivers can be seen from
Apollo 17
to Earth.
One of the biggest mysteries in
astronomy
is where Earth's water came from. Scientists are still trying to answer this question. Earth is special because it is the only
rocky planet
in our
Solar System
with oceans of liquid water on its surface. The other rocky planets,
Mercury
Venus
, and,
Mars
do not have large amounts of liquid water on their surface.
70
Liquid water is important because every living thing we know needs it to survive. Earth has liquid water because it is in just the right spot in space. This spot is called the
habitable zone
. It is not too close to the
Sun
, where water would evaporate. It is also not too far away, where water would freeze. This perfect distance helps keep water in its liquid form on Earth.
71
There are many ideas about how Earth got its water. Most of these ideas fall into two main groups. One idea is that Earth already had the right ingredients (hydrogen and oxygen) when it formed, and those combined to make water. The other idea is that water came from space. It was carried by
asteroids
or
comets
that crashed into Earth after it formed. Some scientists think both of these ideas could be true. Earth might have gotten its water from more than one source. That makes the mystery a bit more complex, but researchers are trying their best to understand what happened in the early Solar System and how water ended up on our planet.
72
73
74
Earth formed about 4.54 billion years ago, after the Sun was born from a huge cloud of gas and dust. The leftover material from that cloud became the rest of the Solar System, including Earth. One idea is that Earth was born with everything it needed to create oceans, lakes, and rivers. But there is a problem. The early Solar System was extremely hot, especially near the center where Earth formed. Any water on the surface would have turned into gas and escaped into
space
75
Another idea is that Earth’s water may have come from deep inside the planet. Water might have been trapped inside rocks deep underground when Earth was forming. This water was safe from the heat because it was hidden inside minerals in Earth's mantle. Over time, volcanoes released that water as steam. When the steam cooled, it turned into rain that helped form oceans and rivers.
76
Another idea is that Earth may have created its own water. Powerful
space telescopes
have seen young
planets
far away, that are surrounded by thick clouds of hydrogen gas. Scientists think that when Earth was very young, it might have had a lot more hydrogen in its atmosphere than it does today. Right now, Earth’s atmosphere is mostly
nitrogen
, and has almost no hydrogen. One idea suggests how hydrogen gas from the atmosphere could react with molten rock (
magma
) on the early Earth. This reaction could have produced large amounts of water. As the surface cooled and hardened, this water would have stayed on the planet, forming oceans and lakes.
77
A long time ago, the inner Solar System was a dangerous place. Between 4.0 and 3.8 billion years ago, the outer planets (
Jupiter
and
Saturn
) moved around and changed their orbits. Their powerful gravity sent icy space rocks flying toward the inner planets, including Earth. This time period is called the
Late Heavy Bombardment
. Many of these space rocks crashed into Earth, and scientists think they could have brought water with them. At first, people thought the water mainly came from comets. But space missions like Giotto (which visited
Halley's Comet
in 1986) and
Rosetta
(which visited another comet from 2014 to 2016) found that the water on comets is different from the water in Earth’s oceans. That means comets probably weren't the main source. Instead, scientists now think
asteroids
and
meteorites
brought most of the water. For example, a spacecraft called Hayabusa2 brought back pieces of an asteroid named Ryugu. Scientists found that the water trapped in its rocks looks like Earth’s ocean water. Ryugu is made of the same stuff as a type of meteorite called CI
chondrites
, which could have delivered up to 30% of the water in Earth’s oceans.
78
79
80
81
This pillow basalt near Hawaii formed when magma came out underwater. Others like it, but much older show that large bodies of water were on Earth a long time ago.
Scientists use ancient rocks to figure out when water first appeared on Earth. One kind of rock they use is called pillow basalt, which forms when a
volcano
erupts underwater. One of these rock was found in the Isua Greenstone Belt in Greenland. It is about 3.8 billion years old. This tells us that there was liquid water on Earth at that time.
82
More of these very old rocks can be found in
Canada
, in a place called the Nuvvuagittuq Greenstone Belt. Some studies of these
rocks
also say there was water about 3.8 billion years old. Other studies suggest there was water 4.28 billion years.
83
If there was water, like oceans, even earlier than that, we don't know yet. That might be because the Earth’s surface is always changing over time. Old rocks can be destroyed or buried through processes like plate
tectonics
and recycling of the crust, which can erase early signs of water. In 2020, scientists suggested that there might have been enough water to fill the oceans immediately after Earth formed.
84
85
86
To understand what Earth was like after it formed, scientists study rocks called
zircons
. Unlike most rocks, zircons are very tough. They can survive for billions of years, making them useful for studying early Earth. Zircons show that there was liquid water and an
atmosphere
4.404 billion years ago, not long after Earth formed.
87
88
89
90
This creates a problem, because the cool early Earth hypothesis says that Earth was cold enough to freeze water between 4.4 and 4.0 billion years ago.
91
Other zircon studies from ancient Australian rocks suggest that plate tectonics may have started around 4 billion years ago.
92
If that's true, Earth may have been similar to today, instead of being hot and covered in carbon dioxide. Plate tectonics helps trap carbon dioxide, which cools the planet and allows solid rock and liquid water to form.
93
In human civilization
change
change source
An aerial view of
irrigation
from the Nile River supporting agriculture in
Egypt
In early human history, people survived by
hunting
animals
and gathering
plants
. They often moved around and stayed close to
sources of water
or carried water around. But about 12 000 years ago, during the
Neolithic revolution
, humans started farming and raising animals. To do this, they needed a steady supply of water. Areas with rich
soil
and regular water made farming possible. This let people settle in one place and live in larger groups. Water also provided
food
, like
fish
and other water animals, and helped people travel using simple
boats
like
canoes
94
95
96
97
The
first human civilizations
began in
river valleys
, where there was plenty of fresh water and good soil for farming. For example,
Mesopotamia
, known as the "Cradle of Civilization," grew between the
Tigris
and
Euphrates
rivers
. People there built
irrigation canals
to bring water to their crops.
98
99
In
Ancient Egypt
, the
Nile river
was very important. It helped people grow food, raise animals, and move goods and people around.
100
101
The
Indus Valley civilization
grew near the
Indus River
. They built advanced water systems, like
wells
drains
, and
public baths
102
103
In
Ancient China
, the
Yellow River
helped northern China grow, but it also flooded a lot and caused many deaths. That is why it was called both "China’s pride" and "China’s sorrow."
104
105
106
In
Ancient Rome
, people built
aqueducts
. They were long channels that carried water from far away places into cities. This water was used for farming, public baths, toilets, and even homes.
107
108
109
In the earliest civilizations,
rivers
and
seas
were very important for transport and trade. They made it easier to move heavy goods over long distances. In Mesopotamia, the Tigris and Euphrates rivers connected cities like
Ur
and
Babylon
110
111
In Egypt, the Nile River helped people trade from
Nubia
in the south all the way to the
Mediterranean Sea
112
113
114
The
Phoenicians
were great sailors who built strong
ships
and set up
trade colonies
around the
Mediterranean
. Busy ports like
Alexandria
Athens
Tyre
, and
Carthage
became rich and full of culture because of sea trade.
115
116
117
118
In
Medieval Europe
, rivers like the
Danube
Rhine
, and
Seine
helped create strong trade networks.
119
120
Cities like
Venice
and
Genoa
became powerful by trading across the sea.
121
122
In the 1400s, countries like
Portugal
Spain
England
, and the
Netherlands
began exploring the world by sea.
Christopher Columbus
’s voyages opened up the
Atlantic Ocean
123
124
This connected
Europe
Africa
, and the
Americas
in what became known as the
Columbian Exchange
. Later, the
British
and the
Dutch East India Company
built huge trade empires using powerful ships and ocean routes.
125
126
As cities got bigger with more people, their
water systems
could not keep up with the growing population. This led to more
disease outbreaks
. This was before people understood how germs worked.
Diseases
like
typhoid
cholera
, and
dysentery
spread quickly through dirty water and killed millions of people over the centuries.
127
In Medieval Europe, cities did not have good
plumbing
. Waste flowed through open sewers in the streets and often mixed with
drinking water
. This caused many deadly epidemics. In the 1800s,
London
had several major cholera outbreaks. At first, people thought the disease came from bad air, called “miasma.” But in 1854, a doctor named John Snow proved that cholera was actually spread through dirty water. He traced the outbreak to a single water pump on Broad Street. People learned that having water was not enough. It had to be clean and kept away from waste. In the late 1800s and early 1900s, cities began improving public health by building better water systems. Engineers created piped water networks, storage tanks, and pumping stations to bring clean water to homes. They also built underground sewer systems to safely carry away human waste. Cities like London,
Paris
, and
New York
only made these changes after big
epidemics
showed how serious the problem was. New
water treatment
methods like
sand filtering
and
adding chlorine
helped kill germs and made water safer to drink.
128
129
130
A long time ago, ancient Greek thinkers like
Thales of Miletus
believed that water was the basic building block of everything in the world.
131
Around 250 BCE,
Archimedes
used water to figure out the
volume
of an object by seeing how much water it pushes away when put in water.
132
During the
Renaissance
Leonardo da Vinci
studied how water flows and how it helps wear away rocks over time. He helped build canals and other things to help control water.
133
Galileo Galilei
looked at why some things float on water and others do not.
134
He also studied
tides
, the regular rising and falling of the sea.
135
By the late 1700s,
Antoine Lavoisier
figured out that water was not an
element
, but a
compound
made from hydrogen and oxygen.
136
Today, about 70% of all the freshwater we use around the world goes to
agriculture
, making farming the biggest user of water. Plants need water to grow, animals need it to live, and
irrigation
helps farmers grow crops even in dry areas.
137
In modern times, how much water a country has can affect whether it can grow enough food for its people or if it has to buy food from other countries. Places with lots of water, like the
United States
Brazil
China
, and
India
, are major food producers. These countries grow extra crops like
wheat
corn
soybeans
, and
rice
, and sell them to other countries. Having lots of rain, rivers, underground water, and good systems like
dams
and
canals
gives these countries a big advantage.
138
But countries with very little water, like
Saudi Arabia
Qatar
, the
UAE
, and
Kuwait
have trouble growing enough food. They do not have enough freshwater or good land for farming, so they import most of their food from other places.
139
Fish
are also an important source of food for the world. Over 1 billion people depend on fish as their main source of protein, especially in places near rivers and oceans.
140
Fish farming, called
aquaculture
, has allowed us to raise fish instead of looking for them.
141
Even today, oceans and rivers are still the main way we move goods around the world. In fact, about 80% of all global trade by volume travels by sea.
142
Oceans, rivers, and canals are great for moving things like fuel, raw materials, and products because it is cheaper than using trucks or planes.
143
Some water routes are especially important. The
Suez Canal
Panama Canal
Strait of Hormuz
, and
Strait of Malacca
are key paths for global trade.
144
Large ports like those in
Shanghai
Rotterdam
Singapore
, and
Los Angeles
help grow their countries' economies.
145
146
Big rivers like the
Mississippi
in the U.S., the
Yangtze
in China, and the
Danube
in Europe are also important. They help move large amounts of goods inside countries cheaply.
147
148
149
Modern water systems help bring clean water to billions of people around the world.
Dams
and
reservoirs
store water for drinking, farming,
flood control
, and even to make
electricity
. Famous examples include the
Hoover Dam
in the U.S. and the
Three Gorges Dam
in China.
150
Pipelines
and
aqueducts
move water from places that have a lot of it to places that do not have much and big cities. For example, Los Angeles gets much of its water from places far away.
151
In very dry regions like the
Middle East
Israel
, and parts of
Australia
, desalination plants turn salty seawater into fresh drinking water. But this process uses a lot of energy.
152
Wastewater treatment plants
clean dirty water from homes and businesses so it does not pollute rivers and lakes. Sometimes, this cleaned water is reused for farming or industry.
153
The world still faces big problems with water. More than 2 billion people live in places where there is not enough water.
154
In areas like India, the southwestern U.S., and the Middle East, people are using up
groundwater
faster than it can be replaced. Because of this, there might not be enough water in the future.
155
Climate change
is making things worse. It causes longer
droughts
, changes where and when rain falls, and reduces the amount of snow in
mountains
Snow
is important because it slowly melts releasing water into rivers over time.
156
Pollution
is also a big problem. Factories, farms, and untreated sewage can make rivers and lakes dirty.
157
Rising sea levels
are pushing saltwater into underground water supplies near the coasts, making them unsafe to drink.
158
More powerful storms are causing
floods
that city drainage systems can not handle.
159
Because of this, we must protect and manage water carefully for the future.
Properties of water
change
change source
A water molecule consists of two hydrogen atoms and one oxygen atom.
Tetrahedral structure of water
Water is a
chemical substance
. It is made of two hydrogen
atoms
and one oxygen atom. Its
chemical formula
is H₂O. These atoms are held together by something called a
covalent bond
. At
room temperature and normal pressure
, water is a liquid. It has almost no color, taste or smell. Water is often called the "universal solvent" because it can dissolve more substances than any other liquid. But it cannot dissolve
nonpolar substances
like
oil
very well. Water is also the only common
material
on Earth that can naturally exist as a solid, liquid, and gas.
33
A water molecule looks like a bent “V” shape. The
angle
between the two hydrogen atoms is about 104.5°. This shape happens because of how
electrons
are arranged around the oxygen atom. Oxygen has six
outer (valence) electrons
. It uses two of them to bond with two hydrogen atoms (one for each). The other four electrons stay in two pairs, called
lone pairs
, that do not bond with anything. According to
VSEPR theory
, all these pairs of electrons want to stay as far apart as possible. This creates a shape like a
tetrahedron
with four regions: two bonding pairs and two lone pairs. But lone pairs take up more space and push harder than bonding pairs. They push the hydrogen atoms closer together, so the angle becomes smaller than the usual 109.5° of a perfect tetrahedron. That is why the water molecule is bent instead of straight, and why the bond angle is 104.5°.
160
161
162
Hydrogen bonds
change
change source
Hydrogen bonds
between molecules of water
A water molecule (H₂O) has one oxygen atom and two hydrogen atoms. Oxygen is much more
electronegative
than hydrogen. This means it attracts electrons closer to itself much more than hydrogen. So, when oxygen and hydrogen share electrons in a water molecule, the electrons spend more time near the oxygen atom. This gives the oxygen atom a partial negative charge (δ⁻). And the hydrogen atoms gains a partial positive charge (δ⁺). So, the water molecule now has a positive side and a negative side. Because of this, the positive hydrogen of one water molecule is attracted to the negative oxygen of another. This attraction is called a
hydrogen bond
. It is not as strong as a normal
chemical bond
(like a
covalent bond
). But, it is strong enough to hold water molecules loosely together. Hydrogen bonding explains many of water’s unusual properties. For example, water's high boiling and
melting points
, high
surface tension
, the ability of ice to float on water, and the ability to dissolve many substances.
160
163
Water (H₂O) is a
liquid
at
room temperature
. This might seem normal until you compare it to similar substances. Water belongs to a group of compounds called
hydrogen chalcogenides
. These are made when hydrogen bonds with elements from the same family as oxygen: sulfur, selenium, and tellurium. This includes
hydrogen sulfide
(H₂S),
hydrogen selenide
(H₂Se), and
hydrogen telluride
(H₂Te). But, while water is a liquid, the others are all gases at room temperature. The reason is hydrogen bonding. Oxygen is very electronegative (it strongly pulls on
electrons
) and is small in size. Because of this, water molecules can form strong hydrogen bonds. Each water molecule can form up to four hydrogen bonds with its neighbors. This creates a kind of "stickiness" that holds the molecules together and makes it harder for them to break apart and turn into a
gas
. That is why water has a high boiling point of 100 °C (212 °F) for such a small molecule. The other
chalcogens
sulfur
selenium
, and
tellurium
) are larger but less electronegative than oxygen. In hydrogen sulfide (H₂S), hydrogen selenide (H₂Se), and hydrogen telluride (H₂Te), the bonds between
hydrogen
and the other elements are weaker. These molecules do not form strong hydrogen bonds. Instead, they only have weak
van der Waals forces
, which are easy to break. So these substances boil at much lower temperatures. Hydrogen sulfide (H₂S) boils at –60 °C. Hydrogen selenide (H₂Se) boils at –41.5 °C. Hydrogen telluride (H₂Te) boils at –2.2 °C. That is why they are gases at room temperature, while water is a liquid.
164
165
166
167
Cohesion and adhesion
change
change source
Water beading on a leaf
Water striders
walk on water because of surface tension
Water molecules stick to each other. This is called
cohesion
. This happens because each water molecule can form hydrogen bonds with its neighbors. Inside a drop of water, each molecule is pulled in all directions by the other water molecules around it. But at the surface, there are no water molecules above. The hydrogen bonds at the surface of water pulls molecules tightly together, forming a sort of "skin" on the surface. This is called
surface tension
. This is why water forms
droplets
. It is also why small
insects
, like water striders, can walk on water. It is also why small objects like a needle can float if placed gently on water.
168
37
169
Water molecules can stick to other surfaces. This is called
adhesion
. This especially happens to surfaces that are polar or charged, like
glass
plant cell walls
, or
soil particles
. Water's adhesion can be seen when water climbs up the side of a glass container, forming a curved surface called the
meniscus
. It can also be seen as water spreads out on a leaf or sticks to surfaces like
spider webs
. Whether water forms flat puddles or round beads depends on the balance between cohesion and adhesion. If water sticks more to the surface, it spreads out. If water sticks more to itself, it forms beads.
170
171
172
Water can climb up a thin tube or narrow space. This is called
capillary action
. It happens because adhesion pulls water molecules to the sides of a thin tube or pore, while cohesion pulls other water molecules along with it.
173
In
plants
, capillary action helps water move from the
roots
to the
leaves
. As water
evaporates
from the leaves, it pulls more water up behind it. Adhesion helps the water stick to the sides of the
plant's tubes
. Cohesion keeps the water molecules connected like a chain, so they move upward together. This allows them to move up against gravity.
174
175
Heat and water
change
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The oceans can store heat helping to keep Earth's temperature stable
Water is very good at staying at the same
temperature
. It does not heat up or cool down quickly. This is because water has a high
specific heat capacity
. That means it takes a lot of heat to make water warmer, and it cools down slowly too. Specific heat is the amount of heat needed to change the temperature of 1 gram of a substance by 1 °C. For water, this is 1
calorie
. That is much higher than most other common substances. For example,
alcohol
only needs 0.6 calories to do the same, so it heats up faster than water.
176
If you touch a
metal pot
with warm water inside, the metal might feel hotter than the water. That is because
metal
heats up faster than water. Water takes longer to warm up because water molecules are held together by hydrogen bonds. When heat is added, much of the energy goes into breaking the hydrogen bonds between water molecules. Once those bonds are broken, the molecules can move faster, and the temperature rises. So instead of heating up quickly, water stores heat by breaking the hydrogen bonds first. When water cools down, the hydrogen bonds form again and release heat. This helps keep temperatures steady. Oceans and lakes can absorb heat from the sun during the
day
or in
summer
and release it slowly at
night
or in
winter
. That is why places near water usually have milder temperatures. Water’s high specific heat also keeps the ocean from getting too hot or too cold. This is very important for ocean life. And because our bodies are mostly made of water, this also helps us keep a steady body temperature.
27
37
177
Water molecules usually stay close together. But if some
molecules
move fast enough, they can break free and escape into the
air
as gas. This process is called
evaporation
. Even at low temperatures, the fastest molecules can still escape. This is why a
glass
of water will slowly disappear over time. Heating water makes its molecules move faster, so it evaporates faster too. The heat of vaporization is the amount of heat needed to turn 1 gram of liquid water into gas. For water, it takes about 580 calories to evaporate just 1 gram at 25 °C. This is nearly double the amount needed for
ammonia
and
alcohol
. Water’s high heat of vaporization is because of hydrogen bonds. Water molecules are held together through hydrogen bonds. To vaporize water, these bonds must be broken, which takes a lot of energy. The energy does not raise the temperature. It goes into breaking the hydrogen bonds. That is why water takes a long time to boil and releases a lot of heat when it condenses.
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37
This high heat of vaporization has important effects on Earth.
Tropical oceans
take in a lot of heat from the Sun. Some of this heat is used to evaporate water. When that water vapor travels to cooler places and turns back into
rain
, it releases heat. This helps balance Earth’s climate and spread heat around the planet.
179
Evaporation also cools things down. When water evaporates, the fastest (hottest) molecules leave first. This lowers the temperature of the water that is left behind. This is called evaporative cooling. It helps keep lakes, plants, and animals from getting too hot. When we
sweat
, the sweat takes heat from our skin as it evaporates. This is why sweating cools down. On hot,
humid
days, the air already has a lot of water vapor. That makes it harder for sweat to evaporate, so we feel even hotter.
180
Some
animals
that cannot sweat, like
elephants
, cool themselves by spraying water on their skin.
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181
It also takes a lot of energy to melt ice. This is called the
heat of fusion
. The heat of fusion is the amount of energy needed to change 1 gram of a substance from solid to liquid at its melting point. For water, this is 334 joules per gram (J/g). That is higher than most other substances, especially for a molecule as small as water. When water freezes into ice, its molecules form a
crystalline structure
held together by hydrogen bonds. To melt ice, you need enough energy to break many of these bonds. The heat added goes into breaking these bonds, but does not increase the temperature. The water that is produced also remains at 0 °C until all of the ice is melted. The same amount of energy needed to melt ice could warm that same ice from –160 °C all the way up to 0 °C. Ice and snow can take in heat without melting right away. This helps keep temperatures from changing too quickly. In cold places like the
North
and
South Poles
or high
mountains
, this helps keep the temperature more steady.
182
Before we had
refrigerators
, people used ice to keep
food
cool because it stayed frozen for a long time.
183
184
185
Density of ice
change
change source
Iceberg
floating on water
Water is one of the only substances that becomes less
dense
when it freezes. This means that ice floats on water. Most substances get smaller and denser when they freeze. But water is different. It expands (or gets bigger) when it freezes. This strange behavior happens because of hydrogen bonds. At temperatures above 4 °C, water acts like most liquids. It expands when heated and shrinks when cooled. But between 4 °C and 0 °C, something strange happens. As the water gets colder, the molecules slow down. They do not have enough energy to break the hydrogen bonds between them. At 0 °C, the molecules line up into a solid crystal shape. Each molecule connects to four others with hydrogen bonds. These bonds hold the molecules further apart. So the ice takes up more space than the liquid water, even though it has the same number of molecules. That is why ice is about 9% less dense than water at 4 °C. When ice melts, the bonds break and the molecules move closer together. Water is densest at 4 °C. It becomes less dense if it gets warmer or cooler from that temperature.
186
24
The fact that ice floats is very important for life on Earth. If ice sank, lakes and oceans could freeze all the way to the bottom. This would make it hard or even impossible for fish and other living things to survive. Instead, ice floats on top, and acts like a blanket. This helps keep the water below from freezing. Fish and other organisms can stay alive under the ice. Also, floating ice provides homes for animals like
polar bears
and
seals
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37
Water as a universal solvent
change
change source
Sodium
ion
from
salt
dissolved in water
When you drop a
sugar cube
into a glass of water, the sugar slowly dissolves and spreads out. This creates a
mixture
. This type of mixture is called a
solution
. In a solution, the
solvent
is the substance that does the dissolving (in this case, water), and the
solute
is the substance that gets dissolved (the sugar). If water is the solvent, the solution is called an
aqueous solution
29
31
37
Water is a very good solvent. Because of this, it is often called the "universal solvent". This is because it can dissolve more substances than any other substance. This happens because water molecules have slightly positive and negative parts. These parts attract other charged or polar substances. For example, when you add salt (sodium chloride, or NaCl) to water, it breaks into sodium (Na⁺) and chloride (Cl⁻) ions. The negative side of water pulls on the sodium, and the positive side pulls on the chloride. Water molecules surround each ion. They then pull them away from the salt crystal. After that, they spread them out in the water. This group of water molecules around an ion is called a
hydration shell
. Other
ionic compounds
, like
potassium chloride
, also dissolve in water this way. Seawater is full of dissolved ions like these. But a substance does not have to be made of ions to dissolve in water. Polar molecules like sugar can also dissolve. This is because they can form hydrogen bonds with water. Even large molecules, like
proteins
, can dissolve in water if they have polar or charged areas on their surfaces.
29
30
32
37
Water is the main solvent for living things. Many important substances are dissolved in the water in
blood
plant sap
, and
cells
. Any substance that mixes well with water is called hydrophilic (water-loving). Some hydrophilic substances do not dissolve in water. For example, some molecules in cells are too big to dissolve. Another example is
cotton
. Cotton is made up of giant molecules of
cellulose
. Cellulose does not dissolve in water. It has lots of positive and negative parts that can form hydrogen bonds with water. Water sticks to the cellulose. That is why cotton
towels
drys things well, but does not dissolve in the
washing machine
. Plants also use cellulose in the
tubes
that carry water from roots to leaves. Water sticks to the hydrophilic walls of these tubes, helping it move upward against gravity. On the other hand, substances that do not mix with water are called hydrophobic (water-fearing). These include
oils
and
fats
. They don't dissolve because they do not have charges that attract water. That is why oil and water do not mix. Hydrophobic molecules can be found in
cell membranes
. Without them, cells would dissolve in water. Life would be impossible.
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31
30
States of water
change
change source
The three common states of matter
Water can exist in three main forms: solid, liquid, and gas. These are called states or phases. Which one water is in depends on the temperature and pressure.
When people say "water" in everyday life, they usually mean liquid water. This is the form that comes from taps, fills oceans, rivers, and lakes, and is used for
drinking
cooking
, and
cleaning
. Liquid water is the most common form found on Earth's surface. When water gets
cold
enough, it freezes and becomes a solid called
ice
. Ice can be in the form of hard cubes (like in your
freezer
) or soft, loose
crystals
, like
snow
. There are also other strange kinds of ice. These are often found in extreme environments like
outer space
deep inside
Uranus
. When water gets hot enough, it turns into a gas called water vapor. This is what we see as steam rising from boiling water.
Water can also exist in a very strange state called a
supercritical fluid
. This only happens at extremely high temperatures above (374 °C or 705 °F) and very high pressures (above 22.064 megapascals). Here, water acts like a gas and a liquid at the same time. It can flow like a liquid and spread out like a gas. Supercritical water is useful because it can dissolve many things that normal water cannot. It can dissolve nonpolar
organic compounds
like oil. This strange state of water does not happen naturally on Earth’s surface. But it can happen deep in the ocean. One example is near
hydrothermal vents
. This happens at around 2200 meters deep. The ocean is much deeper than that on average at about 3800 meters.
187
Changing states
change
change source
Phase diagram of water
Water as a solid, liquid and gas at the same time
A phase diagram is a special
graph
. It shows how a substance like water changes between solid, liquid, and gas depending on the temperature and pressure. On this graph, the bottom (
horizontal
) line shows temperature. The side (
vertical
) line shows pressure. The graph is divided into three parts. One part shows where water is a solid (ice). Another part shows where it is a liquid (water). And another part shows where it is a gas (steam).
188
There is a special point on the graph called the
triple point
. At this temperature and pressure, water can exist as a solid, liquid, and gas at the same time. For water, this happens at 0.01 °C and a pressure of 611.657 pascals.
189
At normal
air pressure
(1 atmosphere), water freezes into ice at 0 °C (32 °F) and boils into steam at 100 °C (212 °F). The
freezing point
is the temperature at which water turns to ice. The
boiling point
is the temperature at which water turns into gas. Water does not need to be boiling to become gas. Even at low temperatures, some water molecules can move fast enough to evaporate. This is why a
glass
of water when left alone will slowly dry out. But when water is heated, the molecules move faster and evaporate quicker. When water reaches 100 °C, bubbles of water vapor form inside the liquid. These bubbles rise to the top and release steam into the air.
29
Water vapor (gas) can turn directly into ice without becoming liquid first. This is called
deposition
. You can see this when frost forms on cold windows. It also happens when
snowflakes
form in clouds. In clouds, tiny pieces of
dust
or
pollen
help water vapor turn straight into ice.
190
The opposite of deposition is called
sublimation
. This is when ice turns straight into water vapor without becoming a liquid.
191
One use of sublimation is in freeze-drying food. a method of
preserving food
. First, the food is frozen. Then it is put into a
vacuum
(a space with no air). The ice inside the food turns into vapor. This leaves the food dry, without using
heat
192
Water usually freezes at 0 °C (32 °F) at normal air pressure. But in special conditions, pure water can stay liquid even it is colder than that. If it is not shaken or disturbed, it can cool all the way down to about –42 °C (–44 °F) without freezing. This is called supercooling.
193
The
melting
and
boiling points
of water change with pressure. For most things, if you add more pressure, they melt at a higher temperature. But water is different because ice is less dense than liquid water. That is why ice floats. When pressure is added to ice, the melting point actually goes down. That means ice can melt even when it is colder than 0 °C if there is enough pressure.
194
This can happen deep under a
glacier
. The heavy ice on top pushes down with a lot of pressure. This pressure can melt the ice under it, even though it is very cold. That is how lakes can form under glaciers.
195
196
Steam (which is water in gas form) takes up much more space than liquid water. That means it is less dense. When the pressure is high, it becomes harder for water to boil, so it needs to be hotter to turn into steam. In places with a lot of pressure, water can stay as a liquid even when it gets hotter than 100 °C (212 °F), which is the normal boiling point.
197
For example, in
geysers
like
Old Faithful
, water can get over 205 °C (401 °F) without boiling.
198
And near underwater volcanoes called
hydrothermal vents
, water can reach 400 °C (752 °F) and still stay liquid.
199
At
sea level
, water boils at 100 °C (212 °F). But when you go up higher like up the
mountains
, the air pressure gets lower. When pressure is lower, water boils at a lower temperature. For every 274 meters (or about 900 feet) you go up, the boiling point goes down by about 1 °C. For example, at 274 meters (about 900 feet), the boiling point becomes 99 °C (210.2 °F) instead of 100 °C (212 °F). That is why food takes longer to cook at higher
altitudes
. The water boils before it gets really hot.
200
pressure cooker
works the opposite way. It traps steam inside, which raises the pressure. This lets water boil at a higher temperature, so food cooks faster.
201
In places with no air at all, like in a vacuum, water can even boil at
room temperature
. This is because there is no pressure holding the water molecules together.
202
Taste and odor
change
change source
People often say that water has no taste or smell.
33
But in real life, most of the water we drink has some
taste
or
smell
. This is because there are usually tiny amounts of other substances dissolved in the water. Pure water does not have a taste, but our tongues can tell if something is mixed in. For example:
Salts
in water can give it a “mineral” taste, like water from
springs
203
204
Water that is very
acidic
tastes sour.
205
Water that is very
basic
(alkaline) tastes bitter.
206
Tap water often has chlorine added to kill germs. This can give it a chemical or medicine-like taste.
207
Metals
like
iron
or
copper
can cause a metallic taste. This can be found in water from old pipes.
208
Even tiny amounts of these substances can change the taste. How strongly people taste them can depend on how cold or warm the water is and even a person's
genes
209
210
Water can smell earthy or musty. This often come from natural chemicals like geosmin or 2-methylisoborneol (MIB) made by
algae
or
bacteria
in lakes and rivers.
211
A rotten egg smell means the water might have
hydrogen sulfide
gas in it.
212
Tap water might smell a little like chlorine, from the
treatment process
Some of these smells are so strong that the
human nose
can detect them even in very small amounts.
213
Some animals, like
frogs
, can even smell water itself.
214
Mechanical properties
change
change source
Water is often called incompressible. This means that even if you push on it really hard, it doesn't shrink much. For example, at the
bottom of the ocean
, about 4 kilometers (2.5 miles) deep, the pressure is 400 times greater than at sea level. But water only gets about 1.8% smaller. This happens because water has a high
bulk modulus
(about 2.2 gigapascals). This means it resists being squeezed.
215
Viscosity
is how easily a liquid flows. Water has low viscosity, so it flows quickly and easily, like in rivers or through pipes.
Honey
or
syrup
have high viscosity, so they flow slowly and are thick. Water flows smoothly through rivers,
pipes
, and the
human body
(like in
blood vessels
and cells). Viscosity changes with temperature. When a liquid gets warmer, it becomes thinner and flows more easily. When it gets colder, it becomes thicker and flows more slowly. So, warm water flows faster, and cold water flows slower. Water is called a
Newtonian fluid
. This means its viscosity stays the same even if you stir it fast or slow.
216
Sound
travels through water at about (1400 to 1540) meters per second, depending on how warm, salty, or deep the water is. That is over 4 times faster than in air.
Whales
use sound to talk and find food underwater. Humans use tools like
sonar
to find things under the sea.
217
218
Electrical properties
change
change source
Animation of the self-ionization of water
Water is a polar molecule. This means it has slightly charged ends. In water molecules, the hydrogen atoms have a small positive charge, and the oxygen atom has a small negative charge. This happens because oxygen pulls electrons closer to itself. That is because oxygen is more
electronegative
. It likes to attract electrons more than hydrogen does. This polarity helps water surround and pull apart other substances, especially those made of charged particles, like table salt (NaCl). When salt is added to water, the negative part of water (the oxygen) surrounds the positive sodium ions (Na⁺). The positive part (the hydrogen) surrounds the negative chloride ions (Cl⁻). This helps break the salt apart and keep the ions floating around in the water.
30
31
Water also has a high
dielectric constant
. It is about 80 at
room temperature
. That is much higher than most other liquids. This means water can reduce the electrical attraction between
opposite charges
. As a result,
ions
(like those from
salt
) can separate more easily in water. This is why it is so good at dissolving
electrolytes
. This makes it easier for ions to stay separate and move around freely. This is important for conducting
electricity
in biological and chemical systems. Thanks to its polarity and
dielectric nature
, water is one of the best solvents in the world. That is why it is called the "universal solvent".
219
Water can go through a special process called autoionization (also called self-ionization). This means that two water molecules can react with each other to make two new particles: a hydronium ion (H₃O⁺) and a hydroxide ion (OH⁻). One water molecule, takes a hydrogen from the other becoming a hydronium ion while the other is left with one hydrogen becoming a hydroxide ion.
219
The
reaction
looks like this:
O + H
+ OH
This reaction does not happen often. At room temperature (25 °C), only a tiny number of water molecules do this. In pure water, the amounts of H₃O⁺ and OH⁻ are each 1 × 10⁻⁷ mol/L (moles per liter). That tiny amount makes water neutral and gives it a
pH
of 7. The pH scale, which tells us if something is acidic or basic, is based on this. Because there are so few ions, pure water does not conduct electricity well. That means pure water is more like an
insulator
than a
conductor
220
But water can dissolve ionic substances like salt very well. When you add even a little table salt (NaCl) to water, it releases lots of ions. The conductivity goes up a million times. That is why
tap water
and
seawater
conduct electricity so well. Seawater, for example, has ions like Na⁺, Cl⁻, and Mg²⁺, making it highly conductive. This matters in real life. Distilled water, which has no ions, can't carry electricity. But regular water, with minerals or salts in it, can carry
electric current
. This is important in
batteries
electrolysis
, and even in cells in your body.
221
Optical properties
change
change source
An indoor swimming pool appears cyan from above, as light reflecting from the bottom of the pool travels through enough water that its red component is absorbed. The same water in a smaller bucket looks only slightly cyan,
222
and observing the water at close range makes it appear colorless to the naked eye.
In small amounts, water looks
clear
, but pure water actually has a slight
blue
tint. You can see the blue color more easily when you look at a large amount of water, like in a
swimming pool
lake
or ocean. The color comes from the way water interacts with light. Pure water absorbs some colors of light more than others. Those colors include the
red
orange
, and
yellow
parts of
sunlight
. This leaves more blue light to be reflected into our
eyes
. This is why water looks blue. You cannot see this in a glass of water. You can only see this when you are looking at deeper water, like in a swimming pool or lake. The deeper the water, the more light gets absorbed, and the more the blue color is seen. If water has something dissolved in it or tiny particles floating in it, the color can change. For example,
algae
and organic matter can make water look green or brown.
Minerals
and
sediments
in the water can change its color.
Tannins
from
decaying
plants can give water a tea-like, brownish color.
223
Visible light
can mostly go through water. Blue and green light go the deepest in water. On the other hand, red, orange, and yellow light gets absorbed by the water, so they do not go very deep. In clear ocean water,
sunlight
can reach down to about 200 meters. This upper layer is called the photic zone. It is where there is enough light for plants and tiny algae like
phytoplankton
to do photosynthesis. Deeper than that, there is not enough light for plants to do photosynthesis.
224
Water bends light because it has a higher
refractive index
than air. The refractive index of water at room temperature (20 °C or 68 °F) is about 1.333. The refractive index of air is about 1.0. This means that when
light
enters water from the air, it slows down and bends. This is called
refraction
. It is this bending of light that causes a straw to look bent or broken in a glass of water. It is also why things under water look closer or larger than they actually are. Ice has a slightly lower refractive index (about 1.31). Because of this, light bends a bit less when passing through ice than through liquid water. The refractive index of water is similar to some liquids like
ethanol
and
alkanes
. But, it is lower than substances like
glycerol
benzene
carbon disulfide
, or
glass
(which range from 1.4 to 1.6). Also, the refractive index of water can change a little depending on the how hot or how cold it is, the pressure, or how much salt is in the water.
225
Chemical reactions of water
change
change source
Water can react with some metals. It reacts with metals more reactive than hydrogen. When this happens, the metal reacts with water to make hydrogen gas and a metal hydroxide. Some metals, like the
alkali metals
(such as
lithium
sodium
, and
potassium
), react very strongly with water. Alkaline earth metals like calcium and magnesium react less violently. For example, sodium reacts violently and makes sodium hydroxide and hydrogen gas:
226
2Na + 2H
O → 2NaOH + H
This reaction gives off a lot of heat (exothermic). It can even cause the hydrogen gas to catch fire.
Water is
amphoteric
. This means it can act like an
acid
or a
base
. This depends on what it is reacting with. When water is with a strong base, it gives away a hydrogen ion (H⁺) and acts like an acid. When water is with a strong acid, it takes in a hydrogen ion and acts like a base.
227
Water can also react with itself in a process called self-ionization:
O + H
20
⇌ H
+ OH
This creates a hydronium ion (H₃O⁺) and a hydroxide ion (OH⁻). This reaction does not happen much in water. It helps set the pH scale, which tells us how acidic or basic a liquid is.
220
Water can also break one
molecule
into two smaller ones in a process called
hydrolysis
. The word comes from Greek: "hydro" meaning water, and "lysis" meaning to break or unbind. In hydrolysis, one molecule breaks into two molecules. A water molecule then breaks apart into a hydrogen ion and a hydroxide ion. The hydrogen ion attaches itself to one of the two new molecules.
228
The hydroxide ion attaches itself to the other molecule. In
industry
, hydrolysis is used to break down compounds like
esters
or
salts
. In biology,
proteins
are broken into
amino acids
through hydrolysis. Fats (lipids) are broken into glycerol and
fatty acids
Carbohydrates
, such as
sucrose
, are broken into simpler
sugars
like
glucose
and
fructose
12
22
11
(sugar) + H
O → C
12
(glucose) + C
12
(fructose)
Hydrolysis is the opposite of a
condensation reaction
. Condensation combines two molecules and releases water. Hydrolysis breaks one molecule into two smaller ones by adding water.
228
Water can be broken down into hydrogen gas (H₂) and oxygen gas (O₂), using a process called
electrolysis
. In this process, an electric current is passed through water that contains small amounts of an electrolyte like
sulfuric acid
or salt. This helps the water conduct electricity. The electricity breaks down the water molecules:
229
2H
O → 2H
+ O
Electrolysis is important because it produces clean
hydrogen fuel
when powered by
renewable energy
like
solar
or
wind
. This is often called
green hydrogen
. It can be used to store
energy
, power
fuel cells
, or replace
fossil fuels
in industry and
transportation
230
On Earth
change
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A graphical distribution of the locations of water on Earth
Visualisation of the distribution of water on Earth (by volume). Each tiny cube (such as the one representing biological water) corresponds to approximately 1 000 km
of water. This amount of water has a mass of about 1 trillion tonnes (200,000 times that of the
Great Pyramid of Giza
or five times that of
Lake Kariba
, arguably the heaviest man-made object). Comprising 1 million tiny cubes, the entire cube would measure about 1 102 km on each side.
Hydrology
is the
science
that studies how water moves, where it is found, and its quality all over the Earth. It is part of a larger group of sciences that study water in different places and forms:
Hydrography
studies where water is located on Earth's surface.
Hydrogeology
focuses on groundwater, water stored underground.
Glaciology
studies ice and glaciers.
Limnology
looks at inland water bodies like lakes and rivers.
Oceanography
studies the oceans.
Ecohydrology
explores how water interacts with
ecosystems
and living things.
All the water on Earth (in oceans, rivers, lakes, ice, underground, and even in the air) is called the
hydrosphere
. The Earth holds about 1.386 billion cubic kilometers of water. Water on Earth is not distributed equally. Most of the water on Earth is found in the oceans. About 96.5% of all the water on Earth is salt water in the oceans. This cannot used for drinking or farming. That leaves only 2.5% of the Earth's water as fresh water. Of this small percentage of freshwater, most of them are in hard to reach places. Around 68.7% of Earth's fresh water is stored in
ice caps
glaciers
, and permanent snow. This is mainly in
Antarctica
and
Greenland
. Another 30.1% is found as
groundwater
, stored in
aquifers
deep under the Earth's surface. This groundwater is an important source of water for
wells
and
springs
. It is very important in
agriculture
and for
drinking
. Only about 1.2% of all fresh water is water that can be found on the surface of the Earth. This includes water in lakes (about 20.9%),
swamps
and
marshes
(2.6%), and rivers (0.49%). Water can also be found in the atmosphere as vapor, clouds, and
precipitation
, and in
soil moisture
, permafrost, and living organisms. But these make up only a tiny fraction of all the water on Earth (less than 0.01%).
19
20
Fresh water is not evenly distributed across the Earth. Some places have more water than others.
Countries
like
Canada
Brazil
, and
Russia
have large supplies of fresh water because of lots of rivers and rainfall. In contrast, dry places like
North Africa
, the
Middle East
, and parts of
Central Asia
have very limited freshwater. Some
tropical
and
temperate
regions get lots of rainfall, while others may go months without much rain.
231
Water cycle
change
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Water cycle
The
water cycle
(also called the hydrologic cycle) is the constant movement of water through the Earth's atmosphere and surface. Water moves between the air, ground, rivers, oceans, lakes, plants, and even underground. The main parts of the water cycle are:
232
Evaporation
: Water from oceans, lakes, and rivers changes into vapor (gas) and rises into the air.
Transpiration
: Plants release water vapor into the air through their leaves.
Condensation
: Water vapor in the air turns into clouds.
Precipitation
: Water vapor in the air cools, turns into liquid or solid, and falls back to Earth as rain, snow, or hail.
Runoff
: Water flows across the land into rivers, lakes, and oceans.
The
sun
is the main source of
energy
that drives the water cycle. When sunlight heats up water, the water molecules move faster and can turn into vapor. This a process called evaporation. This happens in oceans, lakes, rivers, and even from the
land
. Plants also release water vapor through their leaves in a process called transpiration. Together, evaporation and transpiration are called evapotranspiration. The term evapotranspiration is commonly used by
geologists
. Water vapor is invisible to our eyes.
232
Winds
carry water vapor in the atmosphere over long distances. When water vapor cools down, it changes back into liquid water. This is called condensation. This can happen when warm air meets cool air. The water forms tiny drops around dust or salt called condensation nuclei in the air. These drops come together to form clouds. As more droplets stick together, they grow bigger. When they get heavy enough, they fall to Earth as rain,
snow
, or
hail
. This is called precipitation.
232
When precipitation reaches the
ground
, it can do the following. It can evaporate again. It can flow over the land as runoff into rivers and lakes. Or soak into the ground to become groundwater. Water that flows in rivers and lakes is called surface water. Water that moves underground through soil and rock is called groundwater. Groundwater moves slowly and can come back to the surface through
springs
. It can also flow into rivers, lakes, or oceans. This shows how surface water and groundwater are connected.
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Most water that evaporates from the ocean goes back to the ocean. But wind blows water vapor to land at the same rate it goes back to the ocean. Each year, about 47 trillion tons of water vapor move from the ocean to the land. About 72 trillion more tons of water vapor comes from land evaporation and plants. That adds up to 119 trillion tons of precipitation falling on land each year.
233
Precipitation over land has many forms. Most commonly
rain
snow
, and
hail
, with some being
fog
and
dew
. Dew are small drops of water that form when warm, wet air touches a cool surface, usually in the early
morning
. Water droplets in the air may also
refract
sunlight
to produce
rainbows
234
Water that flows over land collects in places called
watersheds
. They then travel through rivers, carving out
valleys
and
deltas
. These areas usually have very good soil, which is good for farming and building cities. Sometimes, too much water causes a
flood
. This can happen when rivers overflow or big storms push water onto the land. Other times, there is not enough water. A
drought
happens when a place gets very little rain for a long time. This is often because of the place or shape of the land.
Water and Earth's geography
change
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Carlsbad caverns in New Mexico, USA has over 119 caves, all formed by water breaking down limestone.
The Stone Forest near Kunming, China has hundreds of tall, sharp towers of limestone shaped by water
Water plays an important role in shaping the Earth’s surface and what is happening under it. It helps form
landscapes
. It breaks down
rocks
. It even affects
volcanic activity
from deep under the surface. Water changes the land through both physical actions, like
erosion
, and
chemical reactions
, like breaking down
minerals
in rocks.
Water plays a big role in breaking down rocks on Earth’s surface. This is a process called
weathering
. There are two main types: physical and chemical. In physical weathering, water gets into cracks in rocks. When it freezes, it expands and makes the cracks bigger. Over time, this causes the rock to break apart. In chemical weathering, water mixes with carbon dioxide from the air or soil. This creates a
weak acid
called
carbonic acid
. Carbonic acid can dissolve some types of rock, especially
limestone
. When this acid gets to limestone underground, it can create large cracks,
caves
, and
tunnels
. On the surface, it can create a type of landscape called
karst
. Here the ground has
sinkholes
, caves, and holes. One amazing example of karst is the
Stone Forest
near
Kunming
China
. It has hundreds of tall, sharp towers of limestone made by water. Another example is
Carlsbad Caverns
in
New Mexico
USA
. This park has over 119 caves, all formed by water breaking down limestone. The biggest one, called the Big Room, is so large it could fit six football fields inside.
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Once rocks are broken down by weathering, the pieces are moved by a process called
erosion
. Water moves bits of rock and minerals away. No rock is strong enough to resist weathering and erosion forever. These powerful forces have created some of Earth’s most famous
landmarks
. For example, the
Grand Canyon
in
Arizona
USA
, was made by the
Colorado River
over millions of years. The canyon is about 446 kilometers (277 miles) long, up to 29 kilometers (18 miles) wide, and about 1.6 kilometers (1 mile) deep.
236
Water is also very good at moving
sediment
. Sediment is made up of small pieces of rock,
sand
, and soil. Rivers, glaciers, rain, and even
ocean currents
move sediment over long distances. Eventually, this sediment settles in new places. Sediment is important because it adds nutrients to the soil. This helps plants grow. Places with lots of sediment, like riverbanks and deltas, are usually great for farming. They have a lot of different plants and animals. For thousands of years, the
Nile River
in
Egypt
flooded every year. This brought about 4 million metric tons of nutrient-rich sediment. Even today, the land next to the Nile is Egypt’s best farmland. Over millions of years, layers of sediment can press together to form
sedimentary rocks
. These rocks can contain
fossils
and clues about Earth’s past, like what the
climate
was like long ago.
237
Deep inside the Earth, water plays an important role in forming
magma
. Magma is the hot, melted rock that can lead to
volcanoes
. The
mantle
is the thick layer under the Earth's crust. It is made of solid rock even though it is hot enough to melt rocks. This is because the pressure deep inside the Earth is so strong that it stops the rock from melting. But in places called
subduction zones
, one of Earth's
tectonic plates
goes under another plate. This brings water down into the mantle. This water lowers the melting point of the rock. This means the rock can start to melt even though it is still under very high pressures. This creates magma, which can rise and cause volcanic eruptions. So, water does not just shape the land on the surface, it also helps cause big changes deep underground. Over millions of years, water has helped shape how Earth looks and behaves.
238
In the Universe
change
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Band 5
ALMA
receiver is an instrument specifically designed to detect water in the universe.
239
Water is not only found on Earth. It can be found all over the
universe
Astronomers
have found ice, vapor, and sometimes liquid water in many places in the universe. Water ice has been found on the
Moon
Mars
, and
comets
. It has also been found on the icy moons of the outer planets, such as
Europa
and
Enceladus
. Even in
interstellar space
, the space between the stars, water exists as ice around tiny dust grains. It also exists as vapor in
molecular clouds
where new
stars
are born. Water has even been found in the atmospheres of
exoplanets
, planets outside our
solar system
A water molecule is made of two hydrogen atoms and one oxygen atom. Hydrogen came from the
Big Bang
. Oxygen was created inside big stars, much larger than the
Sun
. When these stars die and explode, they release oxygen into space. Oxygen can then combine with hydrogen to make water. Huge clouds of gas and dust, called
stellar nurseries
, are where new stars are born. These places often contain huge amounts of water vapor. For example, the
Hubble Space Telescope
found water molecules in the
Helix Nebula
. Water has also been found in young
planetary systems
around other stars. Around the star
Beta Pictoris
, which is about 20 million years old, scientists found water in a giant disk of gas and dust. This is likely from comets smashing into each other, asteroids, and forming planets. In the
Orion Nebula
, one of the biggest and most famous star-forming regions, water is still being made today. It is so large that it makes enough water every day to fill Earth’s oceans 60 times. All of this water, and the other molecules made in these star factories becomes part of new planets.
240
On 22 July 2011, scientists found a gigantic cloud of water vapor that had 140 trillion times more water than the Earth's oceans combined around a
quasar
12 billion light years from Earth. According to the researchers, the discovery shows that water has been in the universe for a very long time.
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242
To find water in space, scientists make use of various tools and techniques.
Telescopes
with
spectrometers
can study the light coming from far away objects. Every molecule absorbs and emits light at specific
wavelengths
. By studying them, scientists can figure out whether there is water.
Radio telescopes
on the ground and
space telescopes
like the Hubble Space Telescope, the
James Webb Space Telescope
, and the
Herschel Space Observatory
have all helped us find water across the universe.
243
244
245
246
247
In our own solar system, spacecraft missions have also been very important.
NASA
’s
Galileo
and
Cassini
missions found strong evidence of subsurface oceans on Jupiter's and Saturn’s moons. Cassini found
geysers
on
Enceladus
, with water vapor and ice particles erupting from the moon’s surface.
248
249
On Mars, orbiters and rovers have found polar ice caps and certain rocks, which suggests that Mars might have had water in the past.
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251
In the solar system
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The gas released from the comet contains water vapor
Model of Europa's possible interior structure, with a thin ice crust and a
subsurface ocean
under it
South polar ice cap of Mars during Martian summer in the year 2000
Water can be found in many places in our Solar System.
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252
Earth is the only planet we know of that has liquid water on its surface all the time. Water can be found as: solid (ice), liquid (water), and gas (water vapor) on Earth. Scientists have found tiny amounts of water vapor in the Sun’s atmosphere. The
Sun
is very hot. Its surface is about 5500 °C (9932 °F) and the inside is even hotter. Normally, water breaks down into hydrogen and oxygen in such heat. But there are cooler spots on the Sun, like
sunspots
. At sunspots, temperatures can drop to about 3000 °C (5432 °F). That is still very hot, but cool enough for water molecules to form for a short time before they break apart into hydrogen and oxygen again.
253
The Moon
and
Mercury
both have water ice hidden in
craters
near their poles. These craters are always in the dark and never get sunlight. Because of this, the ice has stayed frozen for billions of years.
254
255
NASA
spacecrafts
, like the
Lunar Reconnaissance Orbiter
and
MESSENGER
, have found that these ice do exist.
256
257
Venus
has water vapor in its atmosphere, just like Earth. But its surface is very hot and harsh. This means it does not have any liquid water on its surface. Scientists think Venus may have had water in the past, but it was lost into space. This is because Venus does not have a
magnetic field
to protect it like
Earth
does.
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Mars has ice caps at its poles made of water and
carbon dioxide
. There is also ice under the ground in many places.
Rovers
and orbiters have also found
hydrated
minerals
. This means that liquid water once flowed on the surface of Mars a long time ago.
68
Asteroids
are found near a part of the solar system called the “
frost line
”. This is the distance from the Sun where it is cold enough for water to freeze into ice. Beyond this line, you usually won't find liquid water because it is very cold. It can only be found hidden under ice, mixed with salt that keep it from freezing, or trapped under pressure in an atmosphere. One example is
Ceres
, a
dwarf planet
. It may have a layer of dust and rock on the outside, with salty water ice deep under the surface.
259
Asteroids were once thought to be dry, but now scientists have found some that contain water ice or hydrated minerals. NASA’s
OSIRIS-REx
mission is helping us learn more about how much water some asteroids might have.
260
261
Comets
are pieces of ice leftover from the early solar system. They have a lot of frozen water. When a comet gets close to the Sun, the ice turns into gas, creating the famous glowing tails.
262
There also exists a massive cloud of comets called the
Oort cloud
at the edge of the solar system.
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263
The
outer planets
, Jupiter, Saturn, Uranus, and Neptune also have water. They are big gas giants or ice giants. They do not have a solid surface to walk on like our planet.
Jupiter
has water vapor in its thick atmosphere, but it is hard to see because of all the clouds.
264
Saturn
is like Jupiter. It has some water vapor in its atmosphere. Its beautiful rings are mostly made of water ice.
265
Uranus
might have an icy layer deep under its atmosphere.
266
Neptune
is similar to Uranus. Scientists think it also has an icy layer under its atmosphere that may contain water and other ices.
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267
Some of the moons around the giant planets in our Solar System may have huge oceans of liquid water under their frozen surfaces.
Europa
Ganymede
, and
Callisto
, which orbit Jupiter, and
Enceladus
, and
Titan
, which orbit Saturn, might have underground oceans. Enceladus, a small moon of Saturn, shoots out jets of water vapor and ice from its south pole. A spacecraft named
Cassini
flew through these jets and found water, salts, and simple organic molecules. These are clues that there might be a hidden ocean with life. Titan, Saturn’s biggest moon, has lakes and seas on its surface, but they are filled with liquid
methane
and
ethane
, not water. Scientists think Titan has a salty water ocean deep underground, hidden under its icy surface. The moons of Uranus also have icy surfaces.
Titania
, the largest, has water ice and
carbon dioxide ice
. There might be liquid water under its surface.
Triton
, Neptune’s biggest moon, has a surface of frozen water ice. Deep under that ice, scientists also think it might have a liquid ocean.
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268
The dwarf planet
Pluto
has a surface covered in frozen
nitrogen
and water ice. Pluto is extremely cold and far from the Sun. Scientists think Pluto might have a liquid ocean deep beneath its icy crust, about 100 kilometers deep.
269
Pluto’s biggest moon,
Charon
, also has water ice. Beneath the surface, Charon may have had liquid water in the past. Some scientists think ice geysers might still happen on Charon.
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In interstellar space
change
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The Orion Nebula, a molecular cloud where stars are born, contains a huge amount of water mostly in the form of ice
Water is not only found on planets and moons. It can also be found in the vast spaces between stars, the interstellar medium. The
interstellar medium
(ISM), is the scattered mix of gas, dust and
radiation
that can be found in the space between the stars in a
galaxy
. Water can be mainly found as ice covering dust grains in the interstellar medium and dense molecular clouds, where new stars are born. It can also be found as water vapor inside dense molecular clouds. In the coldest parts of the ISM, water molecules condense onto the surfaces of dust grains, forming icy mantles. These icy grains are very important ingredients in the chemistry of making stars and planets.
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271
272
Molecular clouds
, places where stars and planets are born, contain huge amounts of water. Water vapor has been found in many of these clouds, especially near newly forming stars. As young stars fuse
hydrogen
into
helium
they release heat around them. This warms up the surrounding ices, turning them into water vapor. This allows them to be observed by space telescopes such as the
Herschel Space Observatory
and the
Spitzer Space Telescope
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274
One of the most famous places where water has been studied is the
Orion Nebula
. Here, astronomers have found huge amounts of water vapor surrounding stars being born.
275
276
In these environments, water is also very important in the
chemistry
that creates more complex organic molecules like
amino acids
277
64
The
Rho Ophiuchi cloud complex
is a nearby molecular cloud about 460 light-years away. It contains
protostars
surrounded by water-rich ices. The ice in this region has been found using
telescopes
like Spitzer and
JWST
278
279
280
Ice and tiny grains of dust were the main ingredients that came together to form the Solar System. Scientists believe that the water in the solar system formed in space before our Sun or planets even existed. When star systems begin to form,
gravity
pulls together this gas and dust to make stars and planets. The dust already has water on it, which can become part of the new planets. That means planets like Earth might have been born with water already inside them.
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On exoplanets
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Artist's impression of K2-18b
(right)
orbiting
red dwarf
K2-18
(left)
. The
exoplanet
K2-18c
is shown between them. How the planet actually looks like is unknown.
When looking for
life
on other planets, called
exoplanets
, water is one of the most important molecules scientists look for on other planets. We cannot use a telescope to look into other planets for water because they are very far away. But, astronomers have found others ways to look for water on some of these far away planets. The main way scientists study planets outside our Solar System is through something called
transit spectroscopy
. This means watching a planet as it passes in front of its star. When it does, some of the star’s light goes through the planet’s atmosphere to us. Depending on what the atmosphere is made of, certain parts of the light get blocked or bent. This creates a kind of “fingerprint” in the light that scientists can study. By looking closely, they can figure out which gases are in the atmosphere, like water or methane. Right now, studying the atmospheres of exoplanets is still very hard. Our tools are not perfect for this yet and it takes very careful measurements.
282
This method has found water vapor on many "
hot Jupiters
", such as
HD 189733 b
and
HD 209458 b
. These are large
gas giants
very close to their stars. Though these planets are far too hot for liquid water. Water exists as
water vapor
in the atmospheres of these planets.
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In recent years, telescopes have begun finding signs of water on smaller planets, especially
sub-Neptunes
and
super-Earths
. These are planets smaller than gas giants but larger than the Earth. One example is
K2-18b
, a super-Earth found by NASA's Kepler spacecraft in 2015. It is a planet with eight times the mass of the Earth that orbits a so called
red dwarf
star, which is much cooler than the sun. K2-18b can be found in the “
habitable zone
” of its star. This means it has the right temperature to have liquid water. Given its mass and radius, K2-18 b may either be a
rocky planet
with a thick atmosphere or be more like
Neptune
. Observations with Hubble and the James Webb Space Telescope (JWST) have found water vapor in its atmosphere. Though scientists cannot say if it has clouds, oceans, or even rain. Planets in the habitable zone, are places scientists are looking with new technology like the James Webb Space Telescope.
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The search for extraterrestrial life
change
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When scientists look for life in space, they often start by looking for water. Every living thing on Earth needs water to survive. Water has special chemical properties that make it perfect for life. It is really good at dissolving other substances, which helps living things carry out
chemical reactions
. Water stays liquid over a wide range of
temperatures
. It can help keep living organisms from getting too hot or cold. It also helps move nutrients and waste in and out of cells and living organisms. That is why
scientists
often say “follow the water” when searching for life beyond Earth.
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Scientists think moons like Europa (which orbits Jupiter) and Enceladus (which orbits Saturn) might be able to have life. Both moons have thick layers of ice on their surface. Under that ice, scientists believe there are massive
oceans
of liquid water. The bottom of these oceans could be like hydrothermal environments found in the
deep sea
on Earth. On our planet,
hydrothermal vents
release hot, mineral-rich water from under the
seabed
. This creates a place where life thrives without sunlight. Instead of using sunlight for energy (like plants do), the organisms living there use
chemical energy
from the minerals in the water. This is a process called
chemosynthesis
. If similar hydrothermal vents exist on Europa or Enceladus, they could provide the energy and nutrients needed for life to survive in complete darkness, just like Earth’s deep sea life.
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288
Scientists have already found clues supporting these ideas. On Enceladus, for example, NASA’s Cassini spacecraft found jets of water vapor, ice particles, and
organic molecules
shooting out from cracks from the moon. This is a strong sign that there is liquid water and hydrothermal vents under its icy surface. These discoveries make Europa and Enceladus key targets for future space missions.
289
Mars
remains a key target in the search for life beyond Earth. Although the planet is cold and dry today, it shows strong signs that it might have had water in the past. Ancient river valleys, dry lake beds, and minerals that only form in water suggest that liquid water once flowed on the Martian surface. Scientists believe that billions of years ago, Mars may have had a thicker atmosphere and a milder
climate
, possibly making it a habitable world. Even now, there may be salty liquid water hidden underground, especially near the poles or beneath the surface. Briny water, which contains dissolved salts, can stay liquid at colder temperatures, increasing the chances that it might still exist on Mars. To explore this possibility,
NASA
and other space agencies have sent robotic missions like the
Perseverance
and
Curiosity
rovers
to study Mars up close. These rovers have advanced tools to analyze rocks, soil, and even the atmosphere. They are looking for
biosignatures
, which are chemical or physical signs that could suggest past life.
290
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292
Scientists often look for water when they search for life on
exoplanets
. And they often look for planets in the
habitable zone
. This is the area around a star where temperatures are just right for liquid water to exist on a planet. If a planet is too close to its star, it will be too hot and water will boil away. If it is too far, it will be too cold and water will freeze. But in the habitable zone, things can be just right for water to stay liquid. Earth can be found in the habitable zone of the Sun. This is one reason it has oceans, rivers, and rain. That is why it can support so many kinds of life. When scientists study planets around other stars (called exoplanets), they look to see if those planets are also in the habitable zone. If they are, and they have the right kind of atmosphere, they might have water. And, they might even have life. Beyond our
solar system
, astronomers have discovered
water vapor
in the atmospheres of some exoplanets. These findings suggest that water, a key ingredient for life as we know it, might be common in the universe. This ongoing research brings us closer to answering one of the biggest questions in science: Are we alone in the universe?
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Uses of water
change
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Plants
and
animals
(including
people
) are mostly water inside, and must drink water to live. It gives a medium for
chemical reactions
to take place, and is the main part of
blood
. It keeps the
body temperature
the same by
sweating
from the
skin
. Water helps blood carry
nutrients
from the
stomach
to all parts of the body to keep the body alive. Water also helps the blood carry
oxygen
from the
lungs
to the body.
Saliva
, which helps animals and people digest food, is mostly water. Water helps make
urine
. Urine helps remove bad
chemicals
from the body. The human body is between 60% and 70% water, but this value differs with age; i.e. a foetus is 95% water inside.
Water is the main component of
drinks
like
milk
juice
, and
wine
. Each type of drink also has other things that add
flavor
or
nutrients
, things like
sugar
fruit
, and sometimes
alcohol
. Water that a person can drink is called "potable water" (or "drinking water"). The water in oceans is
salt water
, but lakes and rivers usually have
unsalted water
. Only about 3% of all the water on earth is fresh water. The rest is salt water.
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Drop of water falling from a faucet.
Many places, including cities and
deserts
, don't have as much water as people want. They build
aqueducts
to bring water there.
Though people can survive a few months without food, they can only survive for a day or two without water. A few
desert
animals can get enough water from their food, but the others must drink.
Water has no smell, taste, or color.
Water is also used for recreational purposes,
see
list of water sports
Water is used as both the coolant and the
neutron moderator
in most
nuclear reactors
. This may be ordinary water (called light water in the nuclear industry) or
heavy water
Water is also used for washing a lot of objects.
Goods
services
and people are transported to other
countries
in
watercrafts
on bodies of water.
Water is used in
chemical reactions
as a
solvent
or
reactant
. Water is also used in
fire fighting
. Water is also used for
cooking
Water laws, crisis, and geopolitics
change
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Water laws
change
change source
The Colorado River is a river governed by
Prior appropriation water rights
Water laws
are rules that help decide how water is shared, used, and protected. These laws are important because water is something that everyone needs.
People
farms
businesses
, and
nature
all depend on water. Water laws help figure out who can use water, how much they can use, and what they can use it for. They also try to make sure that water is used fairly and not wasted or polluted. In many places, water is limited, and if it is not managed well, it can run out or get too dirty to use. Water laws are meant to stop problems like this including fights over water. They also help make sure there is enough clean water for things like
drinking
, growing
food
, making
energy
, and protecting the
environment
297
Water rights
are the rules about who can use water and how much they can use. These rules are part of water laws.
298
There are different kinds of water rights depending on where you live and the
laws
people follow. One common system is called
riparian rights
, which is often used in places with plenty of water. With riparian rights, if you own land next to a
river
lake
, or
stream
, you have the right to use the water. But you have to be careful not to harm the people who live
downstream
299
In drier places, they often use a different system called
prior appropriation
. This follows the rule of "first in time, first in right." The first person to take water for a useful purpose has the right to keep using it, even if their
land
is not next to the water.
300
In many parts of the world, especially in rural or indigenous communities, customary or traditional laws also guide how water is shared. These laws are based on old practices and
cultural values
that help people respect and protect water.
301
Different
countries
have their own laws and rules for managing water. Some countries focus on deciding who can use water and how they can use it, while others pay more attention to stopping
pollution
or building things like
dams
and
pipelines
to help control water. When rivers, lakes, or underground water cross
borders
between countries, water law becomes more complicated. In these cases, countries need to work together and make agreements to share the water fairly and avoid fights.
302
For example, many countries share big rivers like the
Nile
Mekong
, and
Danube
. These countries cooperate through special agreements to manage the water in a way that works for everyone.
303
Water use is usually managed by national or local governments and special
government agencies
. These groups decide how much water people can use, check that the water is clean and safe, and protect the
plants
and
animals
that need water to live. They also help solve problems when two
communities
or
businesses
want to use the same water source. Water governance means making sure water systems are cared for,
pollution
is controlled. It also means making sure everyone has access to clean water for drinking and
hygiene
. Good water management is very important to handle problems like
droughts
floods
growing populations
, and
climate change
304
There are many important examples of water laws and how they affect people. In the United States, the
Clean Water Act
is a big law that helps protect rivers, lakes, and other water from pollution.
305
In
Africa
, the countries along the Nile River have talked and sometimes argued for a long time about how to share the river’s water fairly.
306
Some countries are starting to say that water is a public good or even a
human right
. This means that everyone should be able to get clean water, no matter how much money they have or who they are.
307
Water crisis
change
change source
drought
happens when there is not enough
rainfall
in an area for a long time
View of flooded
New Orleans
in the aftermath of
Hurricane Katrina
water crisis
is a serious situation that happens when people do not have enough clean and safe water to meet their daily needs for
drinking
cooking
washing
, and
farming
. It also includes times when water is available but too polluted or too far away to be used safely. A water crisis can also affect the
environment
. It can harm
rivers
lakes
, and
plants
and
animals
that depend on water. This problem is not just about having no water at all. It also includes having water that is too dirty, too expensive, or too difficult to reach. There are many reasons why water crises happen.
308
One major cause is
population growth
. As more people are born and the
world’s population
grows, more clean water is needed for drinking, cooking, washing, and growing food. As
cities
get bigger and more people use water, rivers, lakes, and underground water sources are being used up faster than nature can replace it. This causes a water scarcity, which means there is not enough clean water for everyone’s needs. In big cities, the problem can get worse. When lots of people live close together, they all need water at the same time. In
poor
neighborhoods
or fast-growing areas, some people may not have any clean running water at all. In the countryside, farmers use a lot of water to grow crops and feed animals. As the population grows, the demand for
food
grows too, so farmers need even more water. Some use strong
pumps
to pull water from underground, but if they take too much, the water underground can run out.
309
310
311
Another big problem is
pollution
. Even though there is water in rivers, lakes, and oceans, a lot of it is not safe to drink or use because it is polluted. Pollution happens when harmful things like
chemicals
trash
, or dirty water from
homes
and
factories
get into natural water sources. This makes the water dangerous for people, animals, and plants. One major source of pollution is waste from homes and cities. When people wash
dishes
, take
showers
, or flush
toilets
, that dirty water has to go somewhere. In some cities, it goes to special
treatment plants
that clean the water. But in many places around the world, there are no good systems, so the dirty water goes straight into rivers or lakes. This can carry
germs
that cause serious diseases like
cholera
or
diarrhea
. Even in big cities, if the water system breaks or gets too full during a
storm
, dirty water can mix with clean water and make it unsafe to drink. Factories and
farms
also cause a lot of water pollution. Some factories dump leftover chemicals,
oil
, or
heavy metals
into nearby rivers to save
money
. These dangerous substances
poison
the water and can build up in
fish
, making them unsafe to eat. On farms, people use
fertilizers
and
pesticides
to help crops grow and kill bugs. But when it
rains
, these chemicals can wash off the land into rivers or lakes. This is called “water runoff.” It can make
algae
grow too fast. When the algae die, they use up the
oxygen
in the water. Then fish and other animals cannot survive, and parts of the water become
“dead zones”
where nothing can live.
Plastic
is another big problem. Every year, tons of
plastic bottles
bags
, and
wrappers
end up in rivers and oceans. Plastic does not break down easily, so it can float in the water for years. Sea animals like
turtles
or fish might eat
plastic
by mistake and die. Tiny pieces of plastic, called
microplastics
, have even been found in drinking water and
seafood
. Scientists are still studying how these microplastics might affect human health.
312
313
314
315
Another big reason for water problems is overuse. This means people are using too much water too fast, much faster than nature can refill it. Every day, water is needed for many things like drinking, cooking, cleaning, farming, making clothes, building houses, and running factories. As more people live on
Earth
, they use more water. But there is only a limited amount of
fresh water
on the
planet
. When we take too much water without giving
nature
enough time to replace it,
rivers
dry up,
lakes
get smaller, and underground water sources called
aquifers
drop lower and lower.
Farming
uses the most water of all. Farmers need water to grow crops and take care of animals, but in many places, they use more water than necessary. Sometimes they flood their fields, and a lot of the water is wasted or lost to
evaporation
. In dry places, farmers often pump water from deep underground. At first, this works well, but if they keep pumping too much, those underground water supplies start to run out. Once an aquifer is empty, it can take many years or even centuries to fill up again. This is happening in parts of the
United States
India
China
, and many other countries. Factories and industries also use huge amounts of water to make things like
paper
steel
clothes
, and
electronics
. For example, it takes thousands of liters of water to make just one
pair of jeans
or a
hamburger
316
317
318
Another big reason for the water crisis is poor
infrastructure
. Infrastructure means the systems and buildings we use to carry, store, clean, and deliver water, like
pipes
pumps
water treatment plants
, and
storage tanks
. In many places, especially in poorer countries or old cities, these systems are old, broken, or not built well. This means that even if there is enough water nearby, people still cannot get clean, safe water in their homes. Because of this, millions of people either get no water at all or have to use water that can make them sick. In some poor or rural areas, there might be no water system at all, so people have to walk long distances to
rivers
or
wells
to get water by hand. Sometimes this water is not clean because there is no way to filter or clean it. In cities, even when pipes and pumps exist, they may be old and not well cared for. Leaking pipes waste a lot of water, sometimes up to half of it is lost before it even gets to
homes
or
schools
319
In crowded neighborhoods, especially
slums
, water pipes may only work a few hours a day or not at all. People there have to buy water from
trucks
or use unsafe sources. Water treatment plants are supposed to clean the water by removing dirt, germs, and chemicals before people drink it. But if these plants are too small, do not have enough money, or are broken, the water from taps can still be unsafe. Dirty water can cause
diseases
like
cholera
typhoid
, and
diarrhea
, which kill thousands of people every year, especially
children
. Sometimes, clean water and dirty
sewage
use the same underground pipes. When those pipes break or flood, the two can mix, making people sick without them knowing. As more people move to cities, they need more water, but water systems do not always grow fast enough to keep up. During
heat waves
or
droughts
, the systems can break down even more. And during
floods
, water pipes may burst or get clogged, leaving people without water for days.
Another big reason the world has a water crisis is that
governments
often do not
manage water
well. Even if a
country
has enough water, bad
planning
, weak
laws
, and unfair
choices
can cause big problems. In many places, water is not shared fairly. Some people, especially those in rich neighborhoods or powerful
companies
, get plenty of clean water, while others in poor areas get very little or none at all. Sometimes governments build big water projects like
dams
or
canals
, but these only help a few people and leave out whole communities. Poor water planning also causes waste and shortages. In some countries, water is used without limits. Big farms or factories take as much water as they want from rivers or underground, and the government does not keep track of it. This causes overuse, where water is taken faster than
nature
can replace it. Also, water bills may be too cheap or not collected at all, so people do not try to save water. In other places, governments do not spend enough
money
on water systems, so pipes leak, treatment plants break, and many areas have no working water services. Sometimes, powerful people or companies
bribe
officials to get more water than they need, while others are ignored. Governments may promise to build water projects but never finish them, or the money disappears because of
corruption
. Sometimes leaders make decisions without asking local people what they really need, so water projects do not fix real problems. For example, a
city
might build a big water pipeline but forget to build
toilets
or
drains
, which can cause health problems. Another issue is that many governments do not plan for the future. As cities grow and the
climate changes
, water needs change too. But without good planning, old water systems cannot keep up. When
droughts
happen, there are no backup plans. When
floods
come, water systems break down.
At the same time,
climate change
is making the water problem worse. As the
Earth
gets hotter, it changes how water moves in nature. Normally, water falls as
rain
or
snow
, flows into
rivers
and
lakes
, and then evaporates back into the air. But with climate change, this natural
water cycle
gets out of balance. In many places, rain does not come when it is needed, or it falls all at once in
heavy storms
that cause floods. Some areas are getting drier, while others get too much water. This makes it harder for people to get clean and steady water when they really need it. In dry places, climate change causes
droughts
to happen more often and last longer. A drought is when there is very little rain for a long time. This causes rivers to shrink and lakes to dry up.
Crops
would not grow, and animals would not have enough water to drink. Farmers suffer the most because they need water to grow
food
and take care of their
families
. On the other hand, some places get too much water at once. Heavy rain from warmer temperatures can cause floods that destroy homes, farms, and water systems. Flood water can mix with
sewage
and
chemicals
, making it dirty and unsafe to drink. Even though floods bring lots of water, it is often not clean or useful. Also,
glaciers
and
snowpacks
in
mountains
are melting faster than before. These usually act like natural water tanks, slowly releasing water during dry months. But now, they are disappearing, which means millions of people who live downstream will have less water in the future.
The world is facing a very serious water crisis, and the numbers show how big the problem really is. Right now, more than 2.2 billion people, almost 1 out of every 4 people on
Earth
, do not have safe drinking water at home. That means they cannot just turn on a
tap
to get clean water to drink, cook, or wash with. Even more people, about 3.5 billion, do not have proper
sanitation
, like toilets or safe ways to get rid of dirty water. Without clean water and safe toilets,
diseases
spread easily, and many
children
, especially in poor areas, get sick. According to the
World Health Organization
, around 500,000 people die every year from diseases caused by dirty water and poor
hygiene
. About 4 billion people, more than half the world’s population, face serious water shortages for at least one month every year. Some of the countries with the worst water problems include
India
Egypt
Iran
, and parts of the
United States
, like
California
. In these places, rivers are drying up, underground water is running low, and lakes are shrinking. For example, the
Aral Sea
, which used to be one of the largest lakes in the world, has almost completely dried up because people used too much of its water. In
Cape Town
South Africa
, the city almost ran out of water in 2018. The crisis was so bad they called it “Day Zero,” the day the taps would be turned off if water ran out.
Climate change
is making things worse. As the planet gets hotter,
droughts
are happening more often and lasting longer. Rain patterns are changing, so some places get too much rain all at once, causing
floods
, while other places don't get enough rain, leading to dry land and crop failures. The
United Nations
says that by 2050, over 4 billion people might not have safe water at home unless we make big changes. Even in places that have enough water, the systems that deliver it do not always work well. The
World Bank
says the world loses about $260 billion every year because of bad water systems, like leaking pipes, poor planning, or people getting sick and missing work or school because of
waterborne diseases
. At the same time, people living in
slums
or rural areas often have to pay more money per liter for water than rich people in cities. That is because they have to buy it from private sellers or carry it from far away. This is unfair and keeps many families stuck in
poverty
There are many ways we can fix the water crisis, but it takes everyone working together, including
governments
businesses
communities
, and
ordinary people
. One of the most important steps is to build and fix
water systems
. This means making sure
pipes
pumps
treatment plants
, and
tanks
work well and bring clean water to everyone who needs it. In many poor places, there are no water systems at all, so people have to walk far to get water. By investing in strong water systems, clean water can be delivered straight to
homes
schools
, and
hospitals
. Good systems also stop leaks, so less water is wasted before it even reaches people. Another important solution is to use water more carefully and waste less. Many people and factories use more water than they really need. Simple things like fixing dripping taps, taking shorter showers, and turning off the water while brushing your teeth can save a lot of water. Farmers, who use most of the world’s water, can use better methods like
drip irrigation
and
collecting rainwater
to grow crops with less water. In cities,
recycling
water from
sinks
and
showers
to flush
toilets
or water plants helps save even more. Protecting and cleaning our water sources is also very important. Rivers, lakes, and underground water can get polluted by trash, chemicals, and sewage. To keep water clean, we need to stop dumping
waste
into nature. Governments should make strong
laws
to control pollution from factories and farms. People can help too by not throwing garbage into rivers or drains, and by using less plastic and fewer harmful cleaning products. Fair government rules are needed as well. In some places, water is not shared fairly. Rich neighborhoods and big companies get plenty of water, while poor communities get very little. Governments must treat water as a
basic human right
, not just something to buy and sell. They should plan for the future by knowing how much water is available, who needs it most, and how to protect it from climate change. They should also include local people when making decisions about water use and sharing.
Education
is another important part of solving the water crisis. Many people do not know how serious the problem is or what they can do to help.
Schools
TV shows
, and community projects can teach kids and adults about water and why it's important to save it. Finally,
technology
can help a lot. New tools like
water filters
, low-water toilets, smart irrigation systems, and apps that track water use make saving water easier. Even simple tools like tanks that collect rainwater from rooftops can give families clean water in dry areas. Scientists and engineers are working on ways to
clean salty ocean water
, safely recycle wastewater, and watch water use from space. All these ideas together can help make sure there is enough clean water for everyone.
Water geopolitics
change
change source
One of the most well-known water conflicts in the world is happening along the
Nile River
in
Africa
Water is one of the most important resources on
Earth
. People need it to drink, cook, clean, and
grow food
. But when there is not enough water, or when it is not shared fairly, it can lead to
conflict
between people, groups, or even
countries
. One major cause of
water conflict
is
scarcity
. Scarcity means there is not enough water for everyone who needs it. This can happen in dry places where it does not rain much, or in areas where the
population
is growing quickly and using too much water. When water is limited, people may start to argue or fight over who gets to use it. For example, if two
farmers
both use the same
river
to water their
crops
, but the river starts to dry up, they may blame each other and argue about who should get more water. These kinds of problems can happen between
neighborhoods
cities
, or even whole countries that share rivers or lakes.
Another reason people fight over water is when rivers or lakes cross
borders
between countries. These are called
transboundary water sources
, and they can cause serious problems. For example, the
Nile River
flows through several countries in
Africa
. Each country wants to use the water for things like
farming
and
electricity
. If one country builds a
dam
or takes more water than before, the others may get upset or worried they would not have enough. The same kind of conflict happens in other parts of the world.
India
and
Pakistan
have had disagreements over the
Indus River
, and countries in
Central Asia
have argued over rivers that come from melting
mountain glaciers
. If countries do not find fair ways to share the water, it can lead to political fights and even
war
Pollution
is another cause of water conflict. When factories, farms, or cities dump waste into rivers or lakes, the water becomes dirty and unsafe. If one group pollutes the water and another group depends on it for drinking or farming, big problems can happen. People downstream may get sick or lose their crops and blame those upstream. This can lead to
lawsuits
protests
, or even
violence
. Even within one country, different areas or groups might argue about who is polluting the water and who should pay to clean it up. These fights can make it even harder to solve the water crisis.
Unfair sharing of water can also cause problems. In many places, rich neighborhoods or big companies get more water than poor communities. When there is not enough water for everyone, and some people have plenty while others have none, it can make people upset and angry. This can lead to
protests
or even
fights
. For example, in some cities, poor areas called
slums
may have no running water at all. But at the same time, fancy
hotels
nearby might use a lot of water to fill
swimming pools
or run
fountains
. When people see this kind of unfairness, they may feel they are being treated badly and demand change.
Climate change
is also making water conflicts worse. As the
Earth
gets hotter and rain becomes less regular, droughts are happening more often. This puts more stress on water supplies and makes people compete even more. In some places, climate change is melting
glaciers
and drying up rivers. When water becomes harder to find, people worry more and fight harder over the little that is left. If
governments
do not step in to share water fairly and plan for the future, these conflicts could become more serious over time.
One of the most well-known water conflicts in the world is happening along the Nile River in
Africa
. The
Nile
is the longest river in the world, and it flows through 11 different countries, including
Ethiopia
Sudan
South Sudan
Egypt
, and
Uganda
. This river is very important because millions of people use it every day for drinking water, farming, fishing, and making electricity. But since so many countries share the Nile, there are many disagreements about how the water should be divided. The biggest conflict is between Ethiopia, Sudan, and Egypt. Each country depends on the Nile for different reasons, and they do not always agree on what is fair. A major reason for the conflict is a huge
dam
that Ethiopia is building. It is called the
Grand Ethiopian Renaissance Dam
, or GERD. Ethiopia started building this dam in 2011 on the
Blue Nile
, one of the two main branches of the Nile River. Ethiopia says the dam is important because it will create
electricity
for millions of people who do not have enough power. They believe it will help the country grow and develop. However, Egypt is very worried about the dam. Egypt gets about 90% of its water from the Nile, and it fears the dam will lower the amount of water flowing to its farms and cities. Egypt needs the Nile for almost everything, especially to grow crops in the
desert
. Sudan is in the middle. On one hand, the dam could help Sudan by reducing
floods
and giving them more electricity. On the other hand, Sudan is worried that Ethiopia might fill the dam too quickly, which could reduce the amount of water Sudan receives for farming and drinking. Sudan wants all three countries to make a clear
agreement
so that everyone can benefit and no one gets harmed. Ethiopia, Egypt, and Sudan have been talking about this issue for many years, but they still have not made a final deal. Egypt wants strict rules about how and when Ethiopia can fill the dam, especially during dry years. Ethiopia wants to control the dam itself and believes it has the right to use the river that starts in its
land
. Because of these disagreements, there have been many arguments, tense meetings, and even threats. Some people worry that if the countries cannot work together, it could lead to a serious crisis or even conflict.
Another example of water conflict is between
India
and
Pakistan
. These two countries have not always gotten along, and sharing water has made things even more difficult. The
Indus River
and its smaller rivers start in India but flow into Pakistan. In 1960, the two countries signed a
water treaty
to divide the rivers fairly. But even today, each
country
is worried that the other might take more water than they should. When India builds new dams or water projects, Pakistan gets alarmed and accuses India of breaking the agreement. These water issues add to the already tense relationship between the two countries. In the
Middle East
, water is very limited, and this leads to many conflicts. One example is the
Jordan River
, which flows through
Israel
Jordan
, and
Palestine
. All three groups need the river for drinking water, farming, and everyday life. But over the years, the river has shrunk because of overuse and pollution. As the water supply drops, arguments have grown. In the
West Bank
, many Palestinian communities struggle to get enough water, while nearby Israeli settlements often have steady supplies. This unfair access makes people angry and adds to the political tension. Some efforts have been made to share the water more fairly, but it is hard because the groups do not trust each other. In
Yemen
, a country dealing with
war
and
poverty
, water shortages have also led to conflict. Many people there do not have clean water. As
wells
dry up,
villages
and
tribes
sometimes fight over who gets to use the last water sources. In some rural areas, armed groups have taken control of water supplies, making it even harder for families to get the water they need. Some experts believe that water problems have made
Yemen’s civil war
even worse. This shows how lack of water can become even more dangerous when a country is already in crisis.
In the
United States
, water conflicts happen more often than people might think, especially in the
western part of the country
where water is harder to find. One of the biggest and most well-known water fights is over the
Colorado River
. This river flows through seven states:
Colorado
Wyoming
Utah
New Mexico
Arizona
Nevada
, and
California
. It also flows into
Mexico
. More than 40 million people use the Colorado River for drinking water, farming, and making electricity. But lately, the river has been shrinking because of
drought
climate change
, and using too much water. The states argue over how much water each one should get. For example, California uses a lot of water for growing food in the
desert
, while big cities like
Las Vegas
and
Phoenix
need more water as more people move there. The government has tried to help the states make fair deals, but it’s been very hard to agree on a long-term solution. Another big water conflict in the U.S. is between
Georgia
Alabama
, and
Florida
. This fight has been going on for decades. These states share rivers like the
Chattahoochee
and the
Flint
, which come together to form the
Apalachicola River
. Georgia wants more water for the city of
Atlanta
and for farms. But Alabama and Florida say that if Georgia takes too much water, there would not be enough left for them. Florida especially needs the water to keep its seafood industry alive in
Apalachicola Bay
. This fight has gone all the way to the
U.S. Supreme Court
, but even after many years, it is still not solved. Even in places with more water, like around the
Great Lakes
, there can still be conflicts. Some towns and companies want to take more water out of the lakes for their own use, but others worry this could hurt the environment or lower the water levels. The Great Lakes are shared by several
U.S. states
and
Canada
, so any plan to use the water has to be agreed on by everyone. In 2008, a deal called the
Great Lakes Compact
was made to protect the lakes and stop people from taking water unfairly. Still, some places try to find ways around the rules, which causes more arguments and concern.
Even though water can sometimes cause conflict, it can also help bring people together. Many countries, states, and communities have worked hard to cooperate and make fair deals about how to share water. These water
agreements
are very important because they help prevent
arguments
, protect
nature
, and make sure everyone has the water they need. When countries share rivers, lakes, or underground water, they often create
treaties
, or written agreements. These treaties explain how much water each side can use and what to do if there is a problem. They might also include plans to keep the water clean and to stop
pollution
and
waste
. One famous example is the
Indus Waters Treaty
between
India
and
Pakistan
. This treaty was signed in 1960 with help from the
World Bank
. The Indus River system flows through both countries and is very important for farming and daily life. Even though India and Pakistan have had many political problems and even wars, this water treaty has mostly worked well. It divides the rivers between the two countries and includes rules about building dams and using the water fairly. The treaty has helped stop big water fights for over 60 years. This shows that even countries that do not get along can work together when it comes to water.
Another important example of water cooperation is the Senegal River Basin agreement in
West Africa
. The
Senegal River
flows through several countries, including
Senegal
Mali
, and
Mauritania
. In 1972, these countries created a group called the
Organisation for the Development of the Senegal River (OMVS)
. They agreed to manage the river together, share the water fairly, and build dams and power plants that help all the countries. The group listens to farmers, fishermen, and local leaders to make sure everyone’s needs are heard. This kind of
teamwork
helps people trust each other and solve problems peacefully. In
Europe
, there are many rivers that cross between countries. One of the most important is the
Danube River
, which flows through more than 10 countries. In 1994, these countries signed the
Danube River Protection Convention
. They promised to work together to keep the river clean, prevent floods, and protect the plants and animals that live in and around the water. The agreement includes regular meetings, water testing, and teamwork during emergencies. Because of this, the Danube remains safe and helpful for millions of people. The
United Nations (UN)
also supports water cooperation around the world. In 1997, the UN created a special agreement called the
Convention on the Law of the Non-Navigational Uses of International Watercourses
. This set of rules encourages countries to share water fairly, avoid harming each other, and settle arguments peacefully. Not all countries have signed it, but it still helps guide how nations work together to manage shared rivers and lakes. The UN also celebrates
World Water Day
every year on March 22 to remind everyone how important it is to work together on water issues.
In culture
change
change source
In religion
change
change source
A baptism in the
Jordan River
Water has deep meaning in many
cultures
and
religions
around the world. Almost everywhere, water is seen as a symbol of purity,
life
, and change. It often stands for cleansing, not just of the
body
but also of the
spirit
. People believe water can wash away bad things and help start fresh. It is important to many
religious beliefs
and spiritual practices. It can represent the cycle of life, rebirth, and the connection between the physical world and something
sacred
or
divine
. In many
faiths
, water is used in
religious rituals
to bless or purify people. These ceremonies include
baptisms
ritual washings
, and
blessings
. For example, people may wash their hands, face, or whole body before prayer or entering a
sacred place
to show respect and prepare for spiritual contact. In baptism, a person is dipped in or sprinkled with water to mark the start of a spiritual journey. It often means the washing away of
sins
and beginning a new life. Water may also be sprinkled or offered during other
ceremonies
to bless people, objects, or spaces. These practices show the belief that water has spiritual power.
320
321
Different religions use water in special ways. In
Christianity
, baptism is an important ceremony where water is used to show spiritual cleansing and a new life in
Jesus Christ
322
In
Islam
, water is used in
wudu
(a small washing) and
ghusl
(a full-body washing). These are done before
prayers
and other holy activities to be clean in
body
and
spirit
323
324
In
Hinduism
, water is very sacred, especially rivers like the
Ganges
. People believe this river can wash away sins. It is used in many ceremonies, including
funerals
325
326
Buddhists use water in temple rituals as a sign of offering and for spiritual cleansing.
327
In
Judaism
, there is a special bath called a
mikveh
. People use it for
purification
during important times, like before getting
married
or when entering the religion.
328
In
Sikhism
, being clean is part of being spiritual. Sikhs use water for bathing and in some religious rituals.
329
Many
indigenous
and
animist traditions
also see water as sacred.
Rivers
lakes
, and
springs
are believed to be the homes of
spirits
or
gods
. They are often part of rituals and traditional stories.
330
Sacred water sources are very important in many religions. People often travel long distances to visit these special places during
pilgrimages
. These water sites are believed to have healing powers or a spiritual presence.
331
For example, in
Christianity
, many people visit the spring at
Lourdes
in
France
, which is believed to heal the sick. Every year, millions of people go there to pray and collect water.
332
In
Hinduism
, the
Ganges River
is one of the most holy rivers. Bathing in it is believed to wash away sins and bring blessings.
326
In
Islam
, the
Zamzam Well
in
Mecca
is a sacred part of the
Hajj pilgrimage
. It has deep spiritual and historical meaning for Muslims.
333
In philosophy
change
change source
The universe built from a combination of Aristotle's four elements by
Gottfried Wilhelm Leibniz
In ancient times, people believed that everything in the world was made from a few basic things called elements. One of the first known
Western philosophers
Thales of Miletus
, lived in the 6th century BCE and thought that water was the most important of them all. Thales believed that water was the origin of everything. He called it the "archê," a Greek word that means "first principle" or "beginning." He noticed that water is essential for life and can exist in three forms:
solid
liquid
, and
gas
. Because of this, he thought water was the basic building block of the
universe
. Thales was one of the first people to try to understand the world through observation and reason, instead of relying on myths or stories. His ideas helped start what we now call
natural philosophy
, the early form of
science
131
As philosophy grew in different parts of the world, many cultures gave water an important place in their way of thinking. In
ancient Greece
, famous philosophers like
Plato
and
Aristotle
believed that everything was made of four main elements:
earth
air
fire
, and water. Each element had special qualities. Water was thought to be cold and wet. It was linked to change and movement because of the way it flows.
334
In
Eastern philosophy
, water also had deep meaning. In
Daoism
, a major tradition from
China
, water is a symbol of ideal behavior. It flows gently, adapts to its surroundings, and can slowly wear down even hard rock, not by force, but with patience and persistence.
335
This idea is part of the Daoist teaching called
wu wei
, which means acting without effort or force.
336
In
Indian philosophy
, water is one of the
Pancha Mahabhuta
, or five great elements, in both
Hinduism
and
Buddhism
. Water stands for emotion, cleansing, and flow. It is seen as important not just for the body, but also for the soul and the balance of nature.
337
Throughout history, philosophers have used water as a
symbol
or
metaphor
in their writing. Water is often used to represent the flow of time, the way we think and feel, or how things can change shape while staying as the same substance. In many traditions, water stands for change or transformation. It can turn into ice or steam, then go back to being liquid again. Because of this, philosophers use water to talk about how life is always changing, and how nothing stays the same forever. Water is also used to explain how our
identity
(who we are) is not fixed. Like water takes the shape of whatever container it is in, people can be shaped by their surroundings and experiences. In more recent times, philosophers still talk about water in many important ways. In
ecological philosophy
, they explore how people are connected to nature and the environment, and water is a big part of that.
338
In
existentialism
, water can be a symbol for things like uncertainty, deep thoughts, or the search for meaning in life. In
environmental ethics
, water is often discussed in debates about natural rights, fairness, and how to protect the planet. Some modern philosophers believe that water should be seen not just as a resource we use, but as a living system that should be treated with respect and care. Others study how water affects people’s lives, culture, and identity. In a type of philosophy called
phenomenology
, which looks at how we experience the world, water might be studied through the senses. How it feels, looks, sounds, and moves.
339
In folklore
change
change source
The prince thanking the Water sprite, from
The Princess Nobody: A Tale of Fairyland (1884)
by
Andrew Lang
(illustration by
Richard Doyle
Water has been connected to
mythical creatures
and
spirits
in many cultures around the world. Stories often tell of beings like
mermaids
nymphs
kelpies
nāgas
, and other water spirits that live in rivers, lakes, or the ocean. These magical beings are sometimes seen as protectors of water. They might guard a water source and punish people who harm it. In other stories, they may try to trick or lure humans into the water. Some water spirits are wise and kind, offering help or magical advice. Others are tricksters or bring bad luck.
340
In
Japanese folklore
, there is a creature called the
kappa
. Kappa are often seen as water spirits or kami in Japanese folklore. They can act in both mischievous and dangerous ways. Sometimes, they play pranks, like trying to peek under people's clothing near the water. But in other stories, they can be harmful, even trying to drown people or animals or scare children. Even though they can be scary, not all kappa are mean. Some are shown to be friendly and can even help humans.
341
In
Celtic legends
water fairies
are magical beings that live in
rivers
lakes
springs
, and
wells
. They are often connected to
nature
. They are believed to guard the water and its power. These fairies can be kind and helpful, but they can also be tricky or dangerous if they are disrespected.
342
In parts of
Africa
, people believe in
Mami Wata
, a powerful water spirit who can appear as a beautiful woman or a mermaid. She is seen as a guardian of rivers and oceans. Mami Wata protects the natural world. She can bring blessings to those who honor her. But if someone disrespects her, pollutes the water, or breaks a promise, she may punish them.
343
In
Greek mythology
sirens
were dangerous creatures who lived on rocky islands in the sea. They looked like part woman and part bird, but later stories showed them to be more like mermaids. Sirens had beautiful voices and sang songs so sweet that sailors could not resist. The music would lure the sailors closer and closer until their ships crashed on the rocks.
344
In many
myths
and
folktales
, water is seen as a gateway or border between different worlds. Rivers, lakes, and oceans are often shown as dividing lines between the world of the living and the dead, or between the human world and the spirit world. In
Greek mythology
, there is a river called the
Styx
that separates the world of the living from the
underworld
. When someone dies, their
soul
must cross the river to reach the land of the dead. A boatman named
Charon
ferries the souls across, but only if they have a coin to pay him.
345
In
Celtic stories
, lakes and misty waters are often seen as gateways to the
Otherworld
, a magical realm where spirits and fairies live. Some tales say that if you walk into the mist on a quiet lake, you might disappear into another world. The boundary between the worlds is thin near water, especially at
dawn
or
dusk
346
347
In
Japanese folklore
, there is a belief that spirits of the dead must cross a river called the
Sanzu River
to reach the
afterlife
. Like the Greek Styx, it is a border between the living and the dead. Depending on how someone lived their life, they might cross on a bridge, wade through shallow water, or struggle through deep, rough currents.
348
In some Native American traditions, water is a pathway between the physical world and the spirit world.
Shamans
or spiritual leaders may enter a trance near a river or
waterfall
to connect with spirits.
349
In many cultures, water plays an important role in myths about
creation
and destruction. In
Babylonian mythology
, the world began from a vast, dark ocean. Two great water beings,
Apsu
(fresh water) and
Tiamat
(salt water), came together to create the first gods. Later, Tiamat became angry and turned into a monster to destroy them. One of the gods,
Marduk
, defeated her and used her body to form the
sky
and the
earth
350
In the
Bible
, there is the story of
Noah's Ark
, where
God
sends a great
flood
to destroy the world because of human wickedness. The floodwaters cover the earth, wiping out nearly everything. But after the water goes down, life begins again.
351
In
Hindu mythology
, the god
Vishnu
rests on a cosmic ocean before the world is created. From his
navel
grows a
lotus flower
, and from that flower comes
Brahma
, the creator god. Later, when the world becomes evil, Vishnu sends great floods to destroy it and prepare for a new age.
352
In
Norse mythology
, at the end of the world, called
Ragnarök
, giant waves and floods cover the earth as the sea serpent
Jörmungandr
rises from the ocean. Many gods die, and the world is destroyed in water and fire. But after the flood, the world slowly rises again, green and peaceful, ready for a new beginning.
353
In many
myths
and
legends
, water is linked to
healing
and change. People have long believed that special places like sacred springs, wells, and fountains have magical or healing powers. In these stories, someone who drinks the water or bathes in it might be cured of an
illness
, feel stronger, or even gain special abilities. In
Celtic folklore
, there are many stories about sacred wells and springs. These places were believed to be blessed by spirits or ancient gods. People would visit them to wash their wounds or drink the water, hoping to be healed. Some wells were also believed to grant visions or wisdom if the visitor was pure of heart.
354
355
In
Christian tradition
, the waters of
Lourdes
in
France
are said to have healing powers. A young girl named Bernadette saw visions of the
Virgin Mary
near a spring. Since then, millions of people have traveled to Lourdes to bathe in the water or collect it, praying for cures to sickness or pain.
356
In
Japanese mythology
, there are stories of people bathing in hot springs or sacred waterfalls to purify their bodies and spirits. These waters are connected to nature spirits called
kami
, and being near them can bring peace, health, and even a new beginning.
357
In Greek myths, the
fountain of youth
or magical springs could restore a person’s youth and beauty.
Heroes
sometimes went on long journeys to find such water.
358
One famous example is the
River Lethe
, where drinking the water caused people to forget their past, offering a kind of spiritual reset or rebirth.
359
In art
change
change source
The Great Wave off Kanagawa.
Water Lilies
(1907), in the Museum of Fine Arts,
Houston, Texas
Water has been a powerful symbol in
art
for thousands of years. Artists use water to show many different feelings and
ideas
, such as
peace
, change,
danger
, or
mystery
. In
paintings
, water often appears as
oceans
rivers
rain
, or even
tears
. It can be calm and still, like a quiet
lake
, or wild and strong, like crashing
waves
. These
images
help people feel something when they look at the artwork. For example, a peaceful painting of a
pond
might make someone feel relaxed, while a stormy
sea
might show fear or struggle.
360
361
In many cultures, water is also used in art to show
life
and
rebirth
. In
religious art
, water is sometimes shown as holy, like in Christian paintings of
baptisms
, where water is used to wash away sins and begin a new life.
362
In
Hindu
and
Buddhist art
, rivers like the
Ganges
are drawn or carved into temples to show purity and connection to the divine.
363
364
In ancient times, water also appeared in art to show
myths
and
legends
. In
Greek
and
Roman art
, gods like
Poseidon
or
Neptune
were often shown holding
tridents
and riding waves or sea creatures.
365
In
Egyptian art
, the
Nile River
was a symbol of life and was often painted in scenes of farming, fishing, and ceremonies.
366
One famous example of water in art is “
The Great Wave off Kanagawa
” by the Japanese artist
Hokusai
. This
woodblock print
shows a huge, powerful wave towering over small
boats
, with
Mount Fuji
in the background. The wave looks alive, with curling foam like claws, ready to crash down. Even though the image is full of movement and danger, it is also beautifully balanced and carefully designed. Hokusai may have used the sea not just to show nature’s power, but also the strength and struggle of people facing it. This artwork has become one of the most well-known in the world.
367
Another famous painting that shows water is “
Water Lilies
” by the French artist
Claude Monet
. Monet painted many versions of this scene, showing a quiet pond with
lily pads
flowers
, and
reflections
of
trees
and
sky
on the surface of the water. The soft colors and blurred brushstrokes make the paintings feel peaceful and dreamlike. His paintings help people feel calm and connected to nature, like they are standing next to the pond themselves.
368
369
Artists
also use water in more practical ways.
Watercolor painting
, for example, uses water to blend colors in soft, flowing shapes. This kind of painting is known for its light, dreamy look. It is perfect for painting things like
clouds
rain
, or gentle
waves
370
Some modern artists even create art with water itself, such as
fountains
pools
, or water installations that change with movement and time. These works let people see, hear, and even touch the water, making the experience feel alive and special.
371
372
In literature
change
change source
Moby Dick
attacking a
whaling
boat
Water shows up in many
stories
poems
, and
myths
from all over the world. In
books
and other
writing
, water often stands for feelings, life, change, or the unknown.
373
374
One well-known example is in the book
The Old Man and the Sea
by
Ernest Hemingway
. In this story, an old
fisherman
goes out into the
ocean
by himself and tries to catch a huge
fish
. The sea is more than just the place where the story happens. As the fisherman fights to catch the fish, the story talks about human strength, being alone, and having respect for
nature
. The water shows both danger and deep wisdom.
375
In
Moby-Dick
by
Herman Melville
, the ocean is a big part of the story. The book is about Captain Ahab and his crew as they sail across the sea to find a giant white whale named Moby Dick. The ocean is not just where the story takes place, it also stands for big ideas like the unknown, the power of nature, and life’s deepest questions. Captain Ahab becomes obsessed with hunting the
whale
, and this makes the sea feel dangerous and full of madness.
376
In
The Odyssey
by
Homer
, water is a big part of the story. Odysseus, the main
hero
, spends many years sailing across the sea to get home after the
Trojan War
. Along the way, he faces storms, sea monsters, and powerful gods. Each time he travels by water, he faces new problems that test how brave and smart he is. The sea is more than just something to cross, it is a place of adventure, danger, and change. It helps Odysseus grow into a wiser and stronger person. This ancient story shows that water, especially the ocean, was seen as a powerful and magical force, full of meaning and
mystery
377
In
The Secret Garden
by
Frances Hodgson Burnett
, water is shown in a soft and peaceful way. There are moments when
rain
falls and helps bring the
garden
back to life. The rain makes the
flowers
grow and the air feel fresh and clean. For the characters in the story, hearing the rain and feeling the wet earth become signs that things are getting better. The water helps turn the garden from a quiet, lonely place into one that is full of beauty and
happiness
378
In
Huckleberry Finn
by
Mark Twain
, the
Mississippi River
is very important to the story. Huck and Jim, who is an escaped slave, travel down the river on a raft. The river stands for
freedom
and escape. As they float along, they have many adventures, meet different people, and talk about big ideas like right and wrong, and what it means to be a friend. The river is always moving and changing, just like their journey. It gives them time and space to think and grow. Twain uses the river not just as a way to get from place to place, but as a symbol of the characters’ path to better understand themselves and the world around them.
379
In
poetry
, water is often used to show feelings and ideas. In the poem
The Rime of the Ancient Mariner
by
Samuel Taylor Coleridge
, a
sailor
tells a strange and sad story about being lost at sea. The huge ocean around him becomes a symbol of guilt, punishment, and mystery. One famous line from the poem is, “Water, water, every where, And all the boards did shrink; Water, water, every where, nor any drop to drink.” This shows how the ocean, which usually gives life, can also be dangerous and cruel. The poem uses water to teach a lesson, that people must respect nature and the spiritual world.
380
In many
myths
and
legends
, water is part of a journey to another world. In the Greek story of
Orpheus and Eurydice
, Orpheus has to cross a
river
to enter the
underworld
and try to bring back his lost love. The river is a border between life and death, showing that water can mark the edge of what people understand.
381
In an African story about
Mami Wata
, a water spirit appears in
dreams
and visions. She might bring healing, beauty, or riches, but she must be treated with respect.
343
In movies
change
change source
Jaws movie poster
Water is often used in
movies
to create powerful
emotions
, build tension, or act as an challenge for the characters.
Directors
use water in different ways. It can show
danger
mystery
, or
fear
, but it can also show
peace
life
, or change. In
adventure
and
action movies
, water can be exciting or dangerous. It can appear in scenes with
storms
floods
, or
rescues
from
rivers
or
oceans
382
One well-known example is
Titanic (1997)
, where the ocean is not only the
setting
but also a major cause of the
disaster
. At first, the sea looks calm and beautiful, but later, the cold water becomes a threat as the
ship
sinks.
383
In
fantasy
and
science fiction
movies, water can be strange or magical. For example, in
Avatar: The Way of Water
, the ocean is a place full of unusual creatures and emotional moments. It is shown as both a home and a challenge for the
characters
384
In the animated movie
Moana
, water is shown as something that can move on its own and help the
main character
. The ocean guides Moana as she tries to save her
island
. It helps her when she is scared and keeps her safe from harm. In the movie, water acts like a helper. It also links Moana to her
ancestors
, who also sailed the oceans. The ocean in this story is not something to be afraid of but something to understand and rely on. In
Finding Nemo
(2003), the entire story takes place
underwater
. The ocean is full of sea life, reefs, and dangers. It shows that water can be both fun and dangerous. The underwater setting is important to the whole story. In
Cast Away
(2000), the ocean separates the main character from other people after a
plane crash
. The ocean becomes a challenge he must face, and it is also the way he must return to his normal life.
Water is also used in movies to show feelings or deeper meanings. In many
dramas
, rain can show
sadness
being alone
, or a big change in the story. For example, in
The Notebook
, the
rain
scene is full of strong emotion and shows an important moment between two characters. Water can also stand for a new beginning or change. In
horror movies
, water can make scenes more tense or scary. Dark lakes, bathtubs, or storms can trap people or hide something dangerous. In
Jaws
, for example, the ocean looks calm, but a
shark
is hiding below. People swim without knowing the danger, which creates
fear
and
suspense
385
Water also works well in movies because it moves, reflects light, and makes sounds. Whether it is big waves, gentle rain, or quiet ponds, water adds something special to a scene. It helps tell the story in a visual way, sometimes more clearly than words can. This makes water one of the most useful natural elements in
filmmaking
Dihydrogen monoxide parody
change
change source
The
dihydrogen monoxide parody
began as a funny
joke
in the early 1990s. It was meant to show how using big
science
words can confuse people and make safe things sound dangerous. "Dihydrogen monoxide" is just a fancy way of saying water. The word “dihydrogen” means two
hydrogen atoms
, and “monoxide” means one
oxygen atom
. That adds up to H₂O, which is the
chemical formula
for water. Even though it is just water, calling it “dihydrogen monoxide” makes it sound like a harmful
chemical
. This joke was used to show that many people do not always understand science words, and they can be tricked if something is explained in a dramatic or serious-sounding way.
386
One of the earliest and most famous uses of this joke happened in 1997, when a high school student named Nathan Zohner gave a science presentation titled "How Gullible Are We?". In his report, he described all the dangers of “dihydrogen monoxide”. Like causing
burns
(as steam), contributing to
erosion
, being found in
cancer cells
, and even causing death when inhaled. He did not say that it was just water until the very end. Out of 50 students who listened to his presentation, 43 voted to ban the chemical. Nathan’s project became famous, and it showed how people can be easily tricked if they do not have enough
scientific knowledge
or
critical thinking
386
Before that, versions of the joke had appeared in
internet forums
and
emails
, especially as the
internet
was growing in the 1990s. People used the parody to make fun of how the
media
politicians
, or even
environmental activists
might sometimes overreact to scientific information without fully understanding it. Over time, the joke spread widely and became part of
internet culture
. It is often used today in
classrooms
debates
, or
websites
to teach people to read carefully and to question information that sounds too dramatic or scary. The DHMO parody continues to be shared today, often as a reminder that how we present information really matters. If something is said with the right tone, long words, or half-truths, people might believe anything, even that water is dangerous. It is a funny but important lesson in
science literacy
skepticism
, and not jumping to conclusions without understanding the full picture. The website DHMO.org is a joke website which lists the harmful effects of water (DHMO), answers questions, and calls for it to be banned, among other things.
386
387
In music
change
change source
Water has always been a big
inspiration
in
music
because it connects to so many feelings and ideas. People all over the world use water as a symbol in songs to show
emotions
like
peace
sadness
, change,
power
, or even mystery. Just like water can be calm or stormy, music about water can be soft and gentle or loud and intense. For example, a calm river or gentle rain might be used to create a peaceful feeling, while crashing waves or a
flood
might show strong emotions like
anger
heartbreak
, or chaos. Water can represent the flow of life, the passage of time, or the feeling of being overwhelmed by something big.
388
In
classical music
composers
have often used water to paint
pictures
with
sound
. For example, famous composers like
Claude Debussy
wrote pieces such as
La Mer (The Sea)
, where the music was inspired by the sea.
389
Another example is
Frédéric Chopin’s "Raindrop Prelude"
, where repeating notes sound like gentle
raindrops
falling.
390
These pieces do not use words, but the music still makes listeners feel like they are near water. In modern times,
pop
rock
, and
folk songs
also use water in their
lyrics
. Songs like
Bridge Over Troubled Water
by
Simon & Garfunkel
or
River
by
Joni Mitchell
use rivers and storms as ways to talk about emotions and life problems. In these songs, water can be both the problem and the solution. It can pull someone down, or it can wash their
pain
away.
391
392
In many cultures, water is tied to spiritual or emotional cleansing, so music about water is often healing or thoughtful. In African, Asian, and Indigenous traditions, water songs are sometimes sung during
rituals
rain dances
, or
prayers
, asking nature for help or giving thanks for life.
393
394
In
blues music
, rivers often appear as symbols of sorrow or escape, especially in songs from the
American South
, where the
Mississippi River
became a symbol of travel, freedom, and sometimes grief.
395
In reggae and Caribbean music, the sea and rain show up in joyful, laid-back songs that celebrate nature and the rhythm of island life.
396
397
Water even affects how music sounds. In some
electronic
or
ambient music
, water sounds like waves, rain, or dripping are added to create a relaxing background. These sounds are used in
meditation music
or
sleep
playlists
because they help people feel calm and safe.
398
Music therapists
also use water sounds to help people reduce
stress
or connect with their emotions.
399
Related pages
change
change source
Ice
Lake
Life timeline
Nature timeline
Pond
Rain
River
Sea
Steam
Water cycle
Waterway
Water vapor
Notes
change
change source
Vienna Standard Mean Ocean Water
(VSMOW), used for calibration, melts at 273.150 008 9(10) K (0.000 089 (10) °C, and boils at 373.1339
K (99.9839
°C). Other isotopic compositions melt or boil at slightly different temperatures.
A commonly quoted value of 15.7 used mainly in organic chemistry for the pK
of water is incorrect.
10
11
References
change
change source
"naming molecular compounds"
www.iun.edu
. Archived from
the original
on 24 September 2018
. Retrieved
1 October
2018
Sometimes these compounds have generic or common names (e.g., H2O is "water") and they also have systematic names (e.g., H2O, dihydrogen monoxide).
"Definition of Hydrol"
. Merriam-Webster.
Riddick 1970
, Table of Physical Properties, Water 0b. pg 67-8.
sfn error: no target: CITEREFRiddick1970 (
help
Lide 2003
, Properties of Ice and Supercooled Water in Section 6.
sfn error: no target: CITEREFLide2003 (
help
Water
in Linstrom, Peter
J.; Mallard, William
G. (eds.);
NIST Chemistry WebBook, NIST Standard Reference Database Number 69
, National Institute of Standards and Technology, Gaithersburg (MD),
(retrieved 2016-5-27)
Anatolievich, Kiper Ruslan.
"Properties of substance: water"
. Archived from
the original
on 2014-06-02
. Retrieved
2021-02-07
Lide 2003
, Vapor Pressure of Water From 0 to 370 °C in Sec. 6.
sfn error: no target: CITEREFLide2003 (
help
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