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Water

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Chemical compound with formula H2O

A drop of

liquid

water

A block of

solid

water (

ice

)

Clouds

in

Earth’s atmosphere

condense from

gaseous

water vapor

.

Water is an

inorganic

,

transparent

,

tasteless

,

odorless

, and

nearly colorless

chemical substance

, which is the main constituent of

Earth

‘s

hydrosphere

and the

fluids

of all known living

organisms

(in which it acts as a

solvent

[1]

). It is

vital

for all known forms of

life

, even though it provides no

calories

or

organic

nutrients

. Its

chemical formula

is H2O, meaning that each of its

molecules

contains one

oxygen

and two

hydrogen

atoms

, connected by

covalent bonds

. Two hydrogen atoms are attached to one oxygen atom at an angle of 104.45°.

[2]

“Water” is the name of the liquid state of H2O at

standard conditions for temperature and pressure

. It forms

precipitation

in the form of

rain

and

aerosols

in the form of

fog

.

Clouds

consist of suspended droplets of water and

ice

, its solid state. When finely divided,

crystalline

ice may precipitate in the form of

snow

. The gaseous state of water is

steam

or

water vapor

.

Water covers 71% of the

Earth

‘s

surface

, mostly in

seas

and

oceans

.

[3]

Small portions of water occur as

groundwater

(1.7%), in the

glaciers

and the

ice caps

of

Antarctica

and

Greenland

(1.7%), and in the

air

as

vapor

,

clouds

(consisting of ice and liquid water suspended in air), and

precipitation

(0.001%).

[4]

[5]

Water moves continually through the

water cycle

of

evaporation

,

transpiration

(

evapotranspiration

),

condensation

,

precipitation

, and

runoff

, usually reaching the sea.

Water plays an important role in the

world economy

. Approximately 70% of the freshwater used by

humans

goes to

agriculture

.

[6]

Fishing

in salt and fresh water bodies is a major source of food for many parts of the

world

. Much of the long-distance trade of

commodities

(such as oil, natural gas, and manufactured products) is transported by

boats

through

seas

,

rivers

,

lakes

, and

canals

. Large quantities of water, ice, and

steam

are used for

cooling

and

heating

, in

industry

and

homes

. Water is an excellent

solvent

for a wide variety of substances both mineral and organic; as such it is widely used in industrial processes, and in cooking and

washing

. Water, ice and snow are also central to many

sports

and other forms of

entertainment

, such as

swimming

,

pleasure boating

,

boat racing

,

surfing

,

sport fishing

,

diving

,

ice skating

and

skiing

.

Etymology

The word water comes from

Old English

wæter, from

Proto-Germanic

*watar (source also of

Old Saxon

watar,

Old Frisian

wetir,

Dutch

water,

Old High German

wazzar,

German

Wasser, vatn,

Gothic

𐍅𐌰𐍄𐍉 (wato), from

Proto-Indo-European

*wod-or, suffixed form of root *wed- (“water”; “wet”).

[7]

Also

cognate

, through the Indo-European root, with

Greek

ύδωρ (ýdor),

Russian

вода́ (vodá),

Irish

uisce, and

Albanian

ujë.

History

Chemical and physical properties

Water (

H


2

O

) is a

polar

inorganic compound

that is at

room temperature

a

tasteless

and

odorless

liquid, nearly

colorless

with a

hint of blue

. This simplest

hydrogen chalcogenide

is by far the most studied chemical compound and is described as the “universal solvent” for its ability to dissolve many substances.

[8]

[9]

This allows it to be the “

solvent

of life”:

[10]

indeed, water as found in nature almost always includes various dissolved substances, and special steps are required to obtain chemically

pure water

. Water is the only common substance to exist as a

solid

, liquid, and

gas

in normal terrestrial conditions.

[11]

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States

The three common states of matter

Along with oxidane, water is one of the two official names for the chemical compound H
2
O
;

[12]

it is also the

liquid

phase of H
2
O
.

[13]

The other two common

states of matter

of water are the

solid

phase,

ice

, and the gaseous phase,

water vapor

or

steam

. The addition or removal of heat can cause

phase transitions

:

freezing

(water to ice),

melting

(ice to water),

vaporization

(water to vapor),

condensation

(vapor to water),

sublimation

(ice to vapor) and

deposition

(vapor to ice).

[14]

Density

Water differs from most liquids in that it becomes less

dense

as it freezes.

[16]

In 1 atm pressure, it reaches its maximum density of 1,000 kg/m3 (62.43 lb/cu ft) at 3.98 °C (39.16 °F).

[17]

The density of ice is 917 kg/m3 (57.25 lb/cu ft), an expansion of 9%.

[18]

[19]

This expansion can exert enormous pressure, bursting pipes and cracking rocks (see

Frost weathering

).

[20]

In a lake or ocean, water at 4 °C (39.2 °F) sinks to the bottom, and ice forms on the surface, floating on the liquid water. This ice insulates the water below, preventing it from freezing solid. Without this protection, most aquatic organisms would perish during the winter.

[21]

Phase transitions

At a pressure of one

atmosphere

(atm), ice melts or water freezes at 0 °C (32 °F) and water boils or vapor condenses at 100 °C (212 °F). However, even below the boiling point, water can change to vapor at its surface by

evaporation

(vaporization throughout the liquid is known as

boiling

). Sublimation and deposition also occur on surfaces.

[14]

For example,

frost

is deposited on cold surfaces while

snowflakes

form by deposition on an aerosol particle or ice nucleus.

[22]

In the process of

freeze-drying

, a food is frozen and then stored at low pressure so the ice on its surface sublimates.

[23]

The melting and boiling points depend on pressure. A good approximation for the rate of change of the melting temperature with pressure is given by the

Clausius–Clapeyron relation

:

dTdP=T(vL−vS)Lf,{displaystyle {frac {dT}{dP}}={frac {Tleft(v_{text{L}}-v_{text{S}}right)}{L_{text{f}}}},}

where vL{displaystyle v_{text{L}}} and vS{displaystyle v_{text{S}}} are the

molar volumes

of the liquid and solid phases, and Lf{displaystyle L_{text{f}}} is the molar

latent heat

of melting. In most substances, the volume increases when melting occurs, so the melting temperature increases with pressure. However, because ice is less dense than water, the melting temperature decreases.

[15]

In glaciers,

pressure melting

can occur under sufficiently thick volumes of ice, resulting in

subglacial lakes

.

[24]

[25]

The Clausius-Clapeyron relation also applies to the boiling point, but with the liquid/gas transition the vapor phase has a much lower density than the liquid phase, so the boiling point increases with pressure.

[26]

Water can remain in a liquid state at high temperatures in the deep ocean or underground. For example, temperatures exceed 205 °C (401 °F) in

Old Faithful

, a geyser in

Yellowstone National Park

.

[27]

In

hydrothermal vents

, the temperature can exceed 400 °C (752 °F).

[28]

At

sea level

, the boiling point of water is 100 °C (212 °F). As atmospheric pressure decreases with altitude, the boiling point decreases by 1 °C every 274 meters.

High-altitude cooking

takes longer than sea-level cooking. For example, at 1,524 metres (5,000 ft), cooking time must be increased by a fourth to achieve the desired result.

[29]

(Conversely, a

pressure cooker

can be used to decrease cooking times by raising the boiling temperature.

[30]

) In a vacuum, water will boil at room temperature.

[31]

Triple and critical points

Phase diagram of water (simplified)

On a pressure/temperature

phase diagram

(see figure), there are curves separating solid from vapor, vapor from liquid, and liquid from solid. These meet at a single point called the

triple point

, where all three phases can coexist. The triple point is at a temperature of 273.16 K (0.01 °C) and a pressure of 611.657 pascals (0.00604 atm);

[32]

it is the lowest pressure at which liquid water can exist.

Until 2019

, the triple point was used to define the Kelvin temperature scale.

[33]

[34]

The water/vapor phase curve terminates at 647.096 K (373.946 °C; 705.103 °F) and 22.064 megapascals (3,200.1 psi; 217.75 atm).

[35]

This is known as the

critical point

. At higher temperatures and pressures the liquid and vapor phases form a continuous phase called a

supercritical fluid

. It can be gradually compressed or expanded between gas-like and liquid-like densities, its properties (which are quite different from those of ambient water) are sensitive to density. For example, for suitable pressures and temperatures it can

mix freely

with

nonpolar compounds

, including most

organic compounds

. This makes it useful in a variety of applications including high-temperature

electrochemistry

and as an ecologically benign solvent or

catalyst

in chemical reactions involving organic compounds. In Earth’s mantle, it acts as a solvent during mineral formation, dissolution and deposition.

[36]

[37]

Phases of ice and water

The normal form of ice on the surface of Earth is

Ice Ih

, a phase that forms crystals with

hexagonal symmetry

. Another with

cubic crystalline symmetry

,

Ice Ic

, can occur in the upper atmosphere.

[38]

As the pressure increases, ice forms other

crystal structures

. As of 2019, 17 have been experimentally confirmed and several more are predicted theoretically.

[39]

When sandwiched between layers of

graphene

, ice forms a square lattice.

[40]

The details of the chemical nature of liquid water are not well understood; some theories suggest that its unusual behaviour is due to the existence of 2 liquid states.

[17]

[41]

[42]

[43]

Taste and odor

Pure water is usually described as tasteless and odorless, although humans have specific sensors that can feel the presence of water in their mouths,

[44]

and frogs are known to be able to smell it.

[45]

However, water from ordinary sources (including bottled mineral water) usually has many dissolved substances, that may give it varying tastes and odors.

Humans

and other animals have developed senses that enable them to evaluate the

potability

of water by avoiding water that is too salty or

putrid

.

[46]

Color and appearance

Pure water is

visibly

blue due to

absorption

of light in the region ca. 600 nm – 800 nm.

[47]

The color can be easily observed in a glass of tap-water placed against a pure white background, in daylight. The principal absorption bands responsible for the color are

overtones

of the O–H stretching

vibrations

. The apparent intensity of the color increases with the depth of the water column, following

Beer’s law

. This also applies, for example, with a swimming pool when the light source is sunlight reflected from the pool’s white tiles.

In nature, the color may also be modified from blue to green due to the presence of suspended solids or algae.

In industry,

near-infrared spectroscopy

is used with aqueous solutions as the greater intensity of the lower overtones of water means that glass

cuvettes

with short path-length may be employed. To observe the fundamental stretching absorption spectrum of water or of an aqueous solution in the region around 3500 cm−1 (2.85 μm)

[48]

a path length of about 25 μm is needed. Also, the cuvette must be both transparent around 3500 cm−1 and insoluble in water;

calcium fluoride

is one material that is in common use for the cuvette windows with aqueous solutions.

The

Raman-active

fundamental vibrations may be observed with, for example, a 1 cm sample cell.

Aquatic plants

,

algae

, and other

photosynthetic

organisms can live in water up to hundreds of meters deep, because

sunlight

can reach them. Practically no sunlight reaches the parts of the oceans below 1,000 meters (3,300 ft) of depth.

The

refractive index

of liquid water (1.333 at 20 °C (68 °F)) is much higher than that of air (1.0), similar to those of

alkanes

and

ethanol

, but lower than those of

glycerol

(1.473),

benzene

(1.501),

carbon disulfide

(1.627), and common types of glass (1.4 to 1.6). The refraction index of ice (1.31) is lower than that of liquid water.

Polar molecule

Tetrahedral structure of water

In a water molecule, the hydrogen atoms form a 104.5° angle with the oxygen atom. The hydrogen atoms are close to two corners of a tetrahedron centered on the oxygen. At the other two corners are

lone pairs

of valence electrons that do not participate in the bonding. In a perfect tetrahedron, the atoms would form a 109.5° angle, but the repulsion between the lone pairs is greater than the repulsion between the hydrogen atoms.

[49]

[50]

The O–H bond length is about 0.096 nm.

[51]

Other substances have a tetrahedral molecular structure, for example,

methane

(CH
4
) and

hydrogen sulfide

(H
2
S
). However, oxygen is more

electronegative

(holds on to its electrons more tightly) than most other elements, so the oxygen atom retains a negative charge while the hydrogen atoms are positively charged. Along with the bent structure, this gives the molecule an

electrical dipole moment

and it is classified as a

polar molecule

.

[52]

Water is a good polar

solvent

, that dissolves many

salts

and

hydrophilic

organic molecules such as sugars and simple alcohols such as

ethanol

. Water also dissolves many gases, such as oxygen and

carbon dioxide

—the latter giving the fizz of

carbonated

beverages,

sparkling wines

and beers. In addition, many substances in living organisms, such as

proteins

,

DNA

and

polysaccharides

, are dissolved in water. The interactions between water and the subunits of these biomacromolecules shape

protein folding

,

DNA base pairing

, and other phenomena crucial to life (

hydrophobic effect

).

Many organic substances (such as

fats and oils

and

alkanes

) are

hydrophobic

, that is, insoluble in water. Many inorganic substances are insoluble too, including most metal

oxides

,

sulfides

, and

silicates

.

Hydrogen bonding

Model of

hydrogen bonds

(1) between molecules of water

Because of its polarity, a molecule of water in the liquid or solid state can form up to four

hydrogen bonds

with neighboring molecules. Hydrogen bonds are about ten times as strong as the

Van der Waals force

that attracts molecules to each other in most liquids. This is the reason why the melting and boiling points of water are much higher than those of

other analogous compounds

like hydrogen sulfide. They also explain its exceptionally high

specific heat capacity

(about 4.2

J

/g/K),

heat of fusion

(about 333 J/g),

heat of vaporization

(2257 J/g), and

thermal conductivity

(between 0.561 and 0.679 W/m/K). These properties make water more effective at moderating Earth’s

climate

, by storing heat and transporting it between the oceans and the atmosphere. The hydrogen bonds of water are around 23 kJ/mol (compared to a covalent O-H bond at 492 kJ/mol). Of this, it is estimated that 90% is attributable to electrostatics, while the remaining 10% is partially covalent.

[53]

These bonds are the cause of water’s high

surface tension

[54]

and capillary forces. The

capillary action

refers to the tendency of water to move up a narrow tube against the force of

gravity

. This property is relied upon by all

vascular plants

, such as trees.

[55]

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Self-ionisation

Water is a weak solution of hydronium hydroxide – there is an equilibrium 2H
2
O
H
3
O+
+ OH
, in combination with solvation of the resulting

hydronium

ions.

Electrical conductivity and electrolysis

Pure water has a low

electrical conductivity

, which increases with the

dissolution

of a small amount of ionic material such as

common salt

.

Liquid water can be split into the

elements

hydrogen and oxygen by passing an electric current through it—a process called

electrolysis

. The decomposition requires more energy input than the

heat released by the inverse process

(285.8 kJ/

mol

, or 15.9 MJ/kg).

[56]

Mechanical properties

Liquid water can be assumed to be incompressible for most purposes: its compressibility ranges from 4.4 to 5.1×10−10 Pa−1 in ordinary conditions.

[57]

Even in oceans at 4 km depth, where the pressure is 400 atm, water suffers only a 1.8% decrease in volume.

[58]

The

viscosity

of water is about 10−3 Pa·

s

or 0.01

poise

at 20 °C (68 °F), and the

speed of sound

in liquid water ranges between 1,400 and 1,540 meters per second (4,600 and 5,100 ft/s) depending on temperature. Sound travels long distances in water with little attenuation, especially at low frequencies (roughly 0.03

dB

/km for 1 k

Hz

), a property that is exploited by

cetaceans

and humans for communication and environment sensing (

sonar

).

[59]

Reactivity

Metallic elements which are more

electropositive

than hydrogen, particularly the

alkali metals

and

alkaline earth metals

such as

lithium

,

sodium

,

calcium

,

potassium

and

cesium

displace hydrogen from water, forming

hydroxides

and releasing hydrogen. At high temperatures, carbon reacts with steam to form

carbon monoxide

and hydrogen.

On Earth

Hydrology is the study of the movement, distribution, and quality of water throughout the Earth. The study of the distribution of water is

hydrography

. The study of the distribution and movement of groundwater is

hydrogeology

, of glaciers is

glaciology

, of inland waters is

limnology

and distribution of oceans is

oceanography

. Ecological processes with hydrology are in the focus of

ecohydrology

.

The collective mass of water found on, under, and over the surface of a planet is called the

hydrosphere

. Earth’s approximate water volume (the total water supply of the world) is 1.386 × 109 cubic kilometers (3.33 × 108 cubic miles).

[4]

Liquid water is found in

bodies of water

, such as an ocean, sea, lake, river, stream,

canal

, pond, or

puddle

. The majority of water on Earth is

sea water

. Water is also present in the atmosphere in solid, liquid, and vapor states. It also exists as groundwater in

aquifers

.

Water is important in many geological processes. Groundwater is present in most

rocks

, and the pressure of this groundwater affects patterns of

faulting

. Water in the

mantle

is responsible for the melt that produces

volcanoes

at

subduction zones

. On the surface of the Earth, water is important in both chemical and physical

weathering

processes. Water, and to a lesser but still significant extent, ice, are also responsible for a large amount of

sediment transport

that occurs on the surface of the earth.

Deposition

of transported sediment forms many types of

sedimentary rocks

, which make up the

geologic record

of

Earth history

.

Water cycle

Water cycle

The

water cycle

(known scientifically as the hydrologic cycle) refers to the continuous exchange of water within the

hydrosphere

, between the

atmosphere

,

soil

water,

surface water

,

groundwater

, and plants.

Water moves perpetually through each of these regions in the water cycle consisting of the following transfer processes:

  • evaporation

    from oceans and other water bodies into the air and

    transpiration

    from land plants and animals into the air.

  • precipitation

    , from water vapor condensing from the air and falling to the earth or ocean.

  • runoff

    from the land usually reaching the sea.

Most water vapors found mostly in the ocean returns to it, but winds carry water vapor over land at the same rate as runoff into the sea, about 47 

Tt

per year whilst evaporation and transpiration happening in land masses also contribute another 72 Tt per year. Precipitation, at a rate of 119 Tt per year over land, has several forms: most commonly rain, snow, and

hail

, with some contribution from

fog

and

dew

.

[60]

Dew is small drops of water that are condensed when a high density of water vapor meets a cool surface. Dew usually forms in the morning when the temperature is the lowest, just before sunrise and when the temperature of the earth’s surface starts to increase.

[61]

Condensed water in the air may also

refract

sunlight

to produce

rainbows

.

Water runoff often collects over

watersheds

flowing into rivers. A mathematical model used to simulate river or stream flow and calculate water quality parameters is a

hydrological transport model

. Some water is diverted to

irrigation

for agriculture. Rivers and seas offer opportunities for travel and commerce. Through

erosion

, runoff shapes the environment creating river

valleys

and

deltas

which provide rich soil and level ground for the establishment of population centers. A flood occurs when an area of land, usually low-lying, is covered with water which occurs when a river overflows its banks or a storm surge happens. On the other hand, drought is an extended period of months or years when a region notes a deficiency in its water supply. This occurs when a region receives consistently below average precipitation either due to its topography or due to its location in terms of

latitude

.

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Fresh water storage

Water occurs as both “stocks” and “flows.” Water can be stored as lakes, water vapor, groundwater or “aquifers,” and ice and snow. Of the total volume of global freshwater, an estimated 69 percent is stored in glaciers and permanent snow cover; 30 percent is in groundwater; and the remaining 1 percent in lakes, rivers, the atmosphere, and biota.

[62]

The length of time water remains in storage is highly variable: some aquifers consist of water stored over thousands of years but lake volumes may fluctuate on a seasonal basis, decreasing during dry periods and increasing during wet ones. A substantial fraction of the water supply for some regions consists of water extracted from water stored in stocks, and when withdrawals exceed recharge, stocks decrease. By some estimates, as much as 30 percent of total water used for irrigation comes from unsustainable withdrawals of groundwater, causing groundwater depletion.

[63]

Sea water and tides

Sea water

contains about 3.5%

sodium chloride

on average, plus smaller amounts of other substances. The physical properties of seawater differ from

fresh water

in some important respects. It freezes at a lower temperature (about −1.9 °C (28.6 °F)) and its density increases with decreasing temperature to the freezing point, instead of reaching maximum density at a temperature above freezing. The salinity of water in major seas varies from about 0.7% in the

Baltic Sea

to 4.0% in the

Red Sea

. (The

Dead Sea

, known for its ultra-high salinity levels of between 30–40%, is really a

salt lake

.)

Tides

are the cyclic rising and falling of local sea levels caused by the

tidal forces

of the Moon and the Sun acting on the oceans. Tides cause changes in the depth of the marine and

estuarine

water bodies and produce oscillating currents known as tidal streams. The changing tide produced at a given location is the result of the changing positions of the Moon and Sun relative to the Earth coupled with the

effects of Earth rotation

and the local

bathymetry

. The strip of seashore that is submerged at high tide and exposed at low tide, the

intertidal zone

, is an important ecological product of ocean tides.

Effects on life

Overview of

photosynthesis

(green) and

respiration

(red)

From a

biological

standpoint, water has many distinct properties that are critical for the proliferation of life. It carries out this role by allowing

organic compounds

to react in ways that ultimately allow

replication

. All known forms of life depend on water. Water is vital both as a

solvent

in which many of the body’s solutes dissolve and as an essential part of many

metabolic

processes within the body. Metabolism is the sum total of

anabolism

and

catabolism

. In anabolism, water is removed from molecules (through energy requiring enzymatic chemical reactions) in order to grow larger molecules (e.g., starches, triglycerides, and proteins for storage of fuels and information). In catabolism, water is used to break bonds in order to generate smaller molecules (e.g., glucose, fatty acids, and amino acids to be used for fuels for energy use or other purposes). Without water, these particular metabolic processes could not exist.

Water is fundamental to photosynthesis and respiration. Photosynthetic cells use the sun’s energy to split off water’s hydrogen from oxygen.

[64]

Hydrogen is combined with CO2 (absorbed from air or water) to form glucose and release oxygen.[

citation needed

] All living cells use such fuels and oxidize the hydrogen and carbon to capture the sun’s energy and reform water and CO2 in the process (cellular respiration).

Water is also central to acid-base neutrality and enzyme function. An acid, a hydrogen ion (H+, that is, a proton) donor, can be neutralized by a base, a proton acceptor such as a hydroxide ion (OH) to form water. Water is considered to be neutral, with a

pH

(the negative log of the hydrogen ion concentration) of 7.

Acids

have pH values less than 7 while

bases

have values greater than 7.

Aquatic life forms

Earth surface waters are filled with life. The earliest life forms appeared in water; nearly all fish live exclusively in water, and there are many types of marine mammals, such as dolphins and whales. Some kinds of animals, such as

amphibians

, spend portions of their lives in water and portions on land. Plants such as

kelp

and

algae

grow in the water and are the basis for some underwater ecosystems.

Plankton

is generally the foundation of the ocean

food chain

.

Aquatic vertebrates must obtain oxygen to survive, and they do so in various ways. Fish have

gills

instead of

lungs

, although some species of fish, such as the

lungfish

, have both.

Marine mammals

, such as dolphins, whales,

otters

, and

seals

need to surface periodically to breathe air. Some amphibians are able to absorb oxygen through their skin. Invertebrates exhibit a wide range of modifications to survive in poorly oxygenated waters including breathing tubes (see

insect

and

mollusc siphons

) and

gills

(

Carcinus

). However, as invertebrate life evolved in an aquatic habitat most have little or no specialization for respiration in water.

Effects on human civilization

Water

fountain

Civilization has historically flourished around rivers and major waterways;

Mesopotamia

, the so-called cradle of civilization, was situated between the major rivers

Tigris

and

Euphrates

; the ancient society of the

Egyptians

depended entirely upon the

Nile

. The early

Indus Valley Civilization

(c. 3300 BCE to 1300 BCE) developed along the Indus River and tributaries that flowed out of the

Himalayas

.

Rome

was also founded on the banks of the Italian river

Tiber

. Large

metropolises

like

Rotterdam

,

London

,

Montreal

,

Paris

,

New York City

,

Buenos Aires

,

Shanghai

,

Tokyo

,

Chicago

, and

Hong Kong

owe their success in part to their easy accessibility via water and the resultant expansion of trade. Islands with safe water ports, like

Singapore

, have flourished for the same reason. In places such as North Africa and the Middle East, where water is more scarce, access to clean drinking water was and is a major factor in human development.

Health and pollution

An environmental science program – a student from

Iowa State University

sampling water

Water fit for human consumption is called

drinking water

or potable water. Water that is not potable may be made potable by filtration or

distillation

, or by a range of

other methods

. More than 660 million people do not have access to safe drinking water.

[65]

[66]

Water that is not fit for drinking but is not harmful to humans when used for swimming or bathing is called by various names other than potable or drinking water, and is sometimes called

safe water

, or “safe for bathing”. Chlorine is a skin and mucous membrane irritant that is used to make water safe for bathing or drinking. Its use is highly technical and is usually monitored by government regulations (typically 1 part per million (ppm) for drinking water, and 1–2 ppm of chlorine not yet reacted with impurities for bathing water). Water for bathing may be maintained in satisfactory microbiological condition using chemical disinfectants such as

chlorine

or

ozone

or by the use of

ultraviolet

light.

In the US, non-potable forms of

wastewater

generated by humans may be referred to as

grey water

, which is treatable and thus easily able to be made potable again, and

blackwater

, which generally contains

sewage

and other forms of waste which require

further treatment

in order to be made reusable. Greywater composes 50–80% of residential wastewater generated by a household’s sanitation equipment (

sinks

, showers, and kitchen runoff, but not toilets, which generate blackwater.) These terms may have different meanings in other countries and cultures.

Freshwater is a renewable resource, recirculated by the natural

hydrologic cycle

, but pressures over access to it result from the naturally uneven distribution in space and time, growing economic demands by agriculture and industry, and rising populations. Currently, nearly a billion people around the world lack access to safe, affordable water. In 2000, the

United Nations

established the

Millennium Development Goals

for water to halve by 2015 the proportion of people worldwide without access to safe water and

sanitation

. Progress toward that goal was uneven, and in 2015 the UN committed to the

Sustainable Development Goals

of achieving universal access to safe and affordable water and sanitation by 2030. Poor

water quality

and bad sanitation are deadly; some five million deaths a year are caused by water-related diseases. The

World Health Organization

estimates that

safe water

could prevent 1.4 million child deaths from

diarrhoea

each year.

[67]

In the developing world, 90% of all

wastewater

still goes untreated into local rivers and streams.

[68]

Some 50 countries, with roughly a third of the world’s population, also suffer from medium or high water stress and 17 of these extract more water annually than is recharged through their natural water cycles.

[69]

The strain not only affects surface freshwater bodies like rivers and lakes, but it also degrades groundwater resources.

Human uses

Total water withdrawals for agricultural, industrial and municipal purposes per capita, measured in cubic metres (m³) per year in 2010

[70]

Agriculture

The most substantial human use of water is for agriculture, including irrigated agriculture, which accounts for as much as 80 to 90 percent of total human water consumption.

[71]

In the United States, 42% of freshwater withdrawn for use is for irrigation, but the vast majority of water “consumed” (used and not returned to the environment) goes to agriculture.

[72]

Access to fresh water is often taken for granted, especially in developed countries that have build sophisticated water systems for collecting, purifying, and delivering water, and removing wastewater. But growing economic, demographic, and climatic pressures are increasing concerns about water issues, leading to increasing competition for fixed water resources, giving rise to the concept of

peak water

.

[73]

As populations and economies continue to grow, consumption of water-thirsty meat expands, and new demands rise for biofuels or new water-intensive industries, new water challenges are likely.

[74]

An assessment of water management in agriculture was conducted in 2007 by the

International Water Management Institute

in Sri Lanka to see if the world had sufficient water to provide food for its growing population.

[75]

It assessed the current availability of water for agriculture on a global scale and mapped out locations suffering from water scarcity. It found that a fifth of the world’s people, more than 1.2 billion, live in areas of

physical water scarcity

, where there is not enough water to meet all demands. A further 1.6 billion people live in areas experiencing

economic water scarcity

, where the lack of investment in water or insufficient human capacity make it impossible for authorities to satisfy the demand for water. The report found that it would be possible to produce the food required in the future, but that continuation of today’s food production and environmental trends would lead to crises in many parts of the world. To avoid a global water crisis, farmers will have to strive to increase productivity to meet growing demands for food, while industries and cities find ways to use water more efficiently.

[76]

Water scarcity is also caused by production of water intensive products. For example,

cotton

: 1 kg of cotton—equivalent of a pair of jeans—requires 10.9 cubic meters (380 cu ft) water to produce. While cotton accounts for 2.4% of world water use, the water is consumed in regions that are already at a risk of water shortage. Significant environmental damage has been caused: for example, the diversion of water by the former

Soviet Union

from the

Amu Darya

and

Syr Darya

rivers to produce cotton was largely responsible for the disappearance of the

Aral Sea

.

[77]

As a scientific standard

On 7 April 1795, the gram was defined in France to be equal to “the absolute weight of a volume of pure water equal to a cube of one-hundredth of a meter, and at the temperature of melting ice”.

[78]

For practical purposes though, a metallic reference standard was required, one thousand times more massive, the kilogram. Work was therefore commissioned to determine precisely the mass of one liter of water. In spite of the fact that the decreed definition of the gram specified water at 0 °C (32 °F)—a highly reproducible temperature—the scientists chose to redefine the standard and to perform their measurements at the temperature of highest water density, which was measured at the time as 4 °C (39 °F).

[79]

The

Kelvin temperature scale

of the

SI

system was based on the

triple point

of water, defined as exactly 273.16 K (0.01 °C; 32.02 °F), but as of May 2019 is based on the

Boltzmann constant

instead. The scale is an

absolute temperature

scale with the same increment as the Celsius temperature scale, which was originally defined according to the

boiling point

(set to 100 °C (212 °F)) and

melting point

(set to 0 °C (32 °F)) of water.

Natural water consists mainly of the isotopes hydrogen-1 and oxygen-16, but there is also a small quantity of heavier isotopes oxygen-18, oxygen-17, and hydrogen-2 (

deuterium

). The percentage of the heavier isotopes is very small, but it still affects the properties of water. Water from rivers and lakes tends to contain less heavy isotopes than seawater. Therefore, standard water is defined in the

Vienna Standard Mean Ocean Water

specification.

For drinking

A young girl drinking

bottled water

Water availability: the fraction of the population using improved water sources by country

Roadside fresh water outlet from glacier,

Nubra

The

human body

contains from 55% to 78% water, depending on body size.

[80]

To function properly, the body requires between one and seven liters (0.22 and 1.54 imp gal; 0.26 and 1.85 U.S. gal)[

citation needed

] of water per day to avoid

dehydration

; the precise amount depends on the level of activity, temperature, humidity, and other factors. Most of this is ingested through foods or beverages other than drinking straight water. It is not clear how much water intake is needed by healthy people, though the British Dietetic Association advises that 2.5 liters of total water daily is the minimum to maintain proper hydration, including 1.8 liters (6 to 7 glasses) obtained directly from beverages.

[81]

Medical literature favors a lower consumption, typically 1 liter of water for an average male, excluding extra requirements due to fluid loss from exercise or warm weather.

[82]

Healthy kidneys can excrete 0.8 to 1 liter of water per hour, but stress such as exercise can reduce this amount. People can drink far more water than necessary while exercising, putting them at risk of

water intoxication

(hyperhydration), which can be fatal.

[83]

[84]

The popular claim that “a person should consume eight glasses of water per day” seems to have no real basis in science.

[85]

Studies have shown that extra water intake, especially up to 500 milliliters (18 imp fl oz; 17 U.S. fl oz) at mealtime was associated with weight loss.

[86]

[87]

[88]

[89]

[90]

[91]

Adequate fluid intake is helpful in preventing constipation.

[92]

Hazard symbol

for non-potable water

An original recommendation for water intake in 1945 by the Food and Nutrition Board of the

United States National Research Council

read: “An ordinary standard for diverse persons is 1 milliliter for each calorie of food. Most of this quantity is contained in prepared foods.”

[93]

The latest dietary reference intake report by the

United States National Research Council

in general recommended, based on the median total water intake from US survey data (including food sources): 3.7 liters (0.81 imp gal; 0.98 U.S. gal) for men and 2.7 liters (0.59 imp gal; 0.71 U.S. gal) of water total for women, noting that water contained in food provided approximately 19% of total water intake in the survey.

[94]

Specifically, pregnant and

breastfeeding

women need additional fluids to stay hydrated. The

Institute of Medicine

(US) recommends that, on average, men consume 3 liters (0.66 imp gal; 0.79 U.S. gal) and women 2.2 liters (0.48 imp gal; 0.58 U.S. gal); pregnant women should increase intake to 2.4 liters (0.53 imp gal; 0.63 U.S. gal) and breastfeeding women should get 3 liters (12 cups), since an especially large amount of fluid is lost during nursing.

[95]

Also noted is that normally, about 20% of water intake comes from food, while the rest comes from drinking water and beverages (

caffeinated

included). Water is excreted from the body in multiple forms; through

urine

and

feces

, through

sweating

, and by exhalation of water vapor in the breath. With physical exertion and heat exposure, water loss will increase and daily fluid needs may increase as well.

Humans require water with few impurities. Common impurities include metal salts and oxides, including copper, iron, calcium and lead,

[96]

and/or harmful bacteria, such as

Vibrio

. Some

solutes

are acceptable and even desirable for taste enhancement and to provide needed

electrolytes

.

[97]

The single largest (by volume) freshwater resource suitable for drinking is

Lake Baikal

in Siberia.

[98]

Washing

The propensity of water to form

solutions

and

emulsions

is useful in various

washing

processes. Washing is also an important component of several aspects of personal

body hygiene

. Most of the personal water use is due to

showering

, doing the

laundry

and

dishwashing

, reaching hundreds of liters per day per person in developed countries.

Transportation

The use of water for transportation of materials through rivers and canals as well as the international shipping lanes is an important part of the world economy.

Chemical uses

Water is widely used in chemical reactions as a

solvent

or

reactant

and less commonly as a

solute

or

catalyst

. In inorganic reactions, water is a common solvent, dissolving many ionic compounds, as well as other polar compounds such as

ammonia

and

compounds closely related to water

. In organic reactions, it is not usually used as a reaction solvent, because it does not dissolve the reactants well and is

amphoteric

(acidic and basic) and

nucleophilic

. Nevertheless, these properties are sometimes desirable. Also, acceleration of

Diels-Alder reactions

by water has been observed.

Supercritical water

has recently been a topic of research. Oxygen-saturated supercritical water combusts organic pollutants efficiently. Water vapor is used for some processes in the chemical industry. An example is the production of acrylic acid from acrolein, propylene and propane.

[99]

[100]

[101]

[102]

The possible effect of water in these reactions includes the physical-, chemical interaction of water with the catalyst and the chemical reaction of water with the reaction intermediates.

Heat exchange

Water and steam are a common fluid used for

heat exchange

, due to its availability and high

heat capacity

, both for cooling and heating. Cool water may even be naturally available from a lake or the sea. It’s especially effective to transport heat through

vaporization

and

condensation

of water because of its large

latent heat of vaporization

. A disadvantage is that metals commonly found in industries such as steel and copper are

oxidized

faster by untreated water and steam. In almost all

thermal power stations

, water is used as the working fluid (used in a closed-loop between boiler, steam turbine, and condenser), and the coolant (used to exchange the waste heat to a water body or carry it away by

evaporation

in a

cooling tower

). In the United States, cooling power plants is the largest use of water.

[103]

In the

nuclear power

industry, water can also be used as a

neutron moderator

. In most

nuclear reactors

, water is both a coolant and a moderator. This provides something of a passive safety measure, as removing the water from the reactor also

slows the nuclear reaction down

. However other methods are favored for stopping a reaction and it is preferred to keep the nuclear core covered with water so as to ensure adequate cooling.

Fire considerations

Water is used for

fighting

wildfires

.

Water has a high heat of vaporization and is relatively inert, which makes it a good

fire extinguishing

fluid. The evaporation of water carries heat away from the fire. It is dangerous to use water on fires involving oils and organic solvents because many organic materials float on water and the water tends to spread the burning liquid.

Use of water in fire fighting should also take into account the hazards of a

steam explosion

, which may occur when water is used on very hot fires in confined spaces, and of a hydrogen explosion, when substances which react with water, such as certain metals or hot carbon such as coal,

charcoal

, or

coke

graphite, decompose the water, producing

water gas

.

The power of such explosions was seen in the

Chernobyl disaster

, although the water involved did not come from fire-fighting at that time the reactor’s own water cooling system. A steam explosion occurred when the extreme overheating of the core caused water to flash into steam. A hydrogen explosion may have occurred as a result of a reaction between steam and hot

zirconium

.

Some metallic oxides, most notably those of

alkali metals

and

alkaline earth metals

, produce so much heat on reaction with water that a fire hazard can develop. The alkaline earth oxide

quicklime

is a mass-produced substance that is often transported in paper bags. If these are soaked through, they may ignite as their contents react with water.

[104]

Recreation

San Andrés island

,

Colombia

Humans use water for many recreational purposes, as well as for exercising and for sports. Some of these include swimming,

waterskiing

,

boating

,

surfing

and

diving

. In addition, some sports, like

ice hockey

and

ice skating

, are played on ice. Lakesides, beaches and

water parks

are popular places for people to go to relax and enjoy recreation. Many find the sound and appearance of flowing water to be calming, and fountains and other water features are popular decorations. Some keep fish and other flora and fauna inside

aquariums

or ponds for show, fun, and companionship. Humans also use water for snow sports i.e.

skiing

,

sledding

,

snowmobiling

or

snowboarding

, which require the water to be frozen.

Water industry

The

water industry

provides drinking water and

wastewater

services (including

sewage treatment

) to households and industry.

Water supply

facilities include

water wells

,

cisterns

for

rainwater harvesting

,

water supply networks

, and

water purification

facilities,

water tanks

,

water towers

,

water pipes

including old

aqueducts

.

Atmospheric water generators

are in development.

Drinking water is often collected at

springs

, extracted from artificial

borings

(wells) in the ground, or pumped from lakes and rivers. Building more wells in adequate places is thus a possible way to produce more water, assuming the aquifers can supply an adequate flow. Other water sources include rainwater collection. Water may require purification for human consumption. This may involve the removal of undissolved substances, dissolved substances and harmful

microbes

. Popular methods are

filtering

with sand which only removes undissolved material, while

chlorination

and

boiling

kill harmful microbes.

Distillation

does all three functions. More advanced techniques exist, such as

reverse osmosis

.

Desalination

of abundant

seawater

is a more expensive solution used in coastal

arid

climates

.

The distribution of drinking water is done through

municipal water systems

, tanker delivery or as

bottled water

. Governments in many countries have programs to distribute water to the needy at no charge.

Reducing usage by using drinking (potable) water only for human consumption is another option. In some cities such as Hong Kong, seawater is extensively used for flushing toilets citywide in order to

conserve freshwater resources

.

Polluting water

may be the biggest single misuse of water; to the extent that a pollutant limits other uses of the water, it becomes a waste of the resource, regardless of benefits to the polluter. Like other types of pollution, this does not enter standard accounting of market costs, being conceived as

externalities

for which the market cannot account. Thus other people pay the price of water pollution, while the private firms’ profits are not redistributed to the local population, victims of this pollution.

Pharmaceuticals

consumed by humans often end up in the waterways and can have detrimental effects on

aquatic

life if they

bioaccumulate

and if they are not

biodegradable

.

Municipal and industrial wastewater are typically treated at

wastewater treatment plants

. Mitigation of polluted

surface runoff

is addressed through a variety of prevention and treatment techniques. (See

Surface runoff#Mitigation and treatment

.)

Industrial applications

Many industrial processes rely on reactions using chemicals dissolved in water, suspension of solids in water

slurries

or using water to dissolve and extract substances, or to wash products or process equipment. Processes such as

mining

,

chemical pulping

,

pulp bleaching

,

paper manufacturing

, textile production, dyeing, printing, and cooling of power plants use large amounts of water, requiring a dedicated water source, and often cause significant water pollution.

Water is used in

power generation

.

Hydroelectricity

is electricity obtained from

hydropower

. Hydroelectric power comes from water driving a water turbine connected to a generator. Hydroelectricity is a low-cost, non-polluting, renewable energy source. The energy is supplied by the motion of water. Typically a dam is constructed on a river, creating an artificial lake behind it. Water flowing out of the lake is forced through turbines that turn generators.

Three Gorges Dam

is the

largest hydro-electric power station

.

Pressurized water is used in

water blasting

and

water jet cutters

. Also, high pressure water guns are used for precise cutting. It works very well, is relatively safe, and is not harmful to the environment. It is also used in the cooling of machinery to prevent overheating, or prevent saw blades from overheating.

Water is also used in many industrial processes and machines, such as the

steam turbine

and

heat exchanger

, in addition to its use as a chemical

solvent

. Discharge of untreated water from industrial uses is

pollution

. Pollution includes discharged solutes (chemical pollution) and discharged coolant water (

thermal pollution

). Industry requires pure water for many applications and utilizes a variety of purification techniques both in water supply and discharge.

Food processing

Water can be used to cook foods such as

noodles

Sterile water for injection

Boiling

,

steaming

, and

simmering

are popular cooking methods that often require immersing food in water or its gaseous state, steam.

[105]

Water is also used for

dishwashing

. Water also plays many critical roles within the field of

food science

.

Solutes

such as salts and sugars found in water affect the physical properties of water. The boiling and freezing points of water are affected by solutes, as well as

air pressure

, which is in turn affected by altitude. Water boils at lower temperatures with the lower air pressure that occurs at higher elevations. One

mole

of sucrose (sugar) per kilogram of water raises the boiling point of water by 0.51 °C (0.918 °F), and one mole of salt per kg raises the boiling point by 1.02 °C (1.836 °F); similarly, increasing the number of dissolved particles lowers water’s freezing point.

[106]

Solutes in water also affect water activity that affects many chemical reactions and the growth of microbes in food.

[107]

Water activity can be described as a ratio of the vapor pressure of water in a solution to the vapor pressure of pure water.

[106]

Solutes in water lower water activity—this is important to know because most bacterial growth ceases at low levels of water activity.

[107]

Not only does microbial growth affect the safety of food, but also the preservation and shelf life of food.

Water hardness

is also a critical factor in food processing and may be altered or treated by using a chemical ion exchange system. It can dramatically affect the quality of a product, as well as playing a role in sanitation. Water hardness is classified based on concentration of calcium carbonate the water contains. Water is classified as soft if it contains less than 100 mg/l (UK)

[108]

or less than 60 mg/l (US).

[109]

According to a report published by the Water Footprint organization in 2010, a single kilogram of beef requires 15 thousand liters (3.3×10^3 imp gal; 4.0×10^3 U.S. gal) of water; however, the authors also make clear that this is a global average and circumstantial factors determine the amount of water used in beef production.

[110]

Medical use

Water for injection is on the

World Health Organization’s list of essential medicines

.

[111]

Distribution in nature

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In the universe

Band 5

ALMA

receiver is an instrument specifically designed to detect water in the universe.

[112]

Much of the universe’s water is produced as a byproduct of

star formation

. The formation of stars is accompanied by a strong outward wind of gas and dust. When this outflow of material eventually impacts the surrounding gas, the shock waves that are created compress and heat the gas. The water observed is quickly produced in this warm dense gas.

[113]

On 22 July 2011, a report described the discovery of a gigantic cloud of water vapor containing “140 trillion times more water than all of Earth’s oceans combined” around a

quasar

located 12 billion light years from Earth. According to the researchers, the “discovery shows that water has been prevalent in the universe for nearly its entire existence”.

[114]

[115]

Water has been detected in

interstellar clouds

within our

galaxy

, the

Milky Way

.

[116]

Water probably exists in abundance in other galaxies, too, because its components, hydrogen, and oxygen, are among the most abundant elements in the universe. Based on models of the

formation and evolution of the Solar System

and that of other star systems, most other

planetary systems

are likely to have similar ingredients.

Water vapor

Water is present as vapor in:

  • Atmosphere of the Sun

    : in detectable trace amounts

    [117]

  • Atmosphere of Mercury

    : 3.4%, and large amounts of water in

    Mercury’s

    exosphere

    [118]

  • Atmosphere of Venus

    : 0.002%

    [119]

  • Earth’s atmosphere

    : ≈0.40% over full atmosphere, typically 1–4% at surface; as well as

    that of the Moon

    in trace amounts

    [120]

  • Atmosphere of Mars

    : 0.03%

    [121]

  • Atmosphere of Ceres

    [122]

  • Atmosphere of Jupiter

    : 0.0004%

    [123]

    – in

    ices

    only; and that of its moon

    Europa

    [124]

  • Atmosphere of Saturn

    – in

    ices

    only;

    Enceladus

    : 91%

    [125]

    and

    Dione

    (exosphere)[

    citation needed

    ]

  • Atmosphere of Uranus

    – in trace amounts below 50 bar

  • Atmosphere of Neptune

    – found in the deeper layers

    [126]

  • Extrasolar planet

    atmospheres: including those of

    HD 189733 b

    [127]

    and

    HD 209458 b

    ,

    [128]

    Tau Boötis b

    ,

    [129]

    HAT-P-11b

    ,

    [130]

    [131]

    XO-1b

    ,

    WASP-12b

    ,

    WASP-17b

    , and

    WASP-19b

    .

    [132]

  • Stellar atmospheres

    : not limited to cooler stars and even detected in giant hot stars such as

    Betelgeuse

    ,

    Mu Cephei

    ,

    Antares

    and

    Arcturus

    .

    [131]

    [133]

  • Circumstellar disks

    : including those of more than half of

    T Tauri stars

    such as

    AA Tauri

    [131]

    as well as

    TW Hydrae

    ,

    [134]

    [135]

    IRC +10216

    [136]

    and

    APM 08279+5255

    ,

    [114]

    [115]

    VY Canis Majoris

    and

    S Persei

    .

    [133]

Liquid water

Liquid water is present on Earth, covering 71% of its surface.

[3]

Liquid water is also occasionally present in small amounts

on Mars

.

[137]

Scientists believe liquid water is present in the Saturnian moons of

Enceladus

, as a 10-kilometre thick ocean approximately 30–40 kilometres below Enceladus’ south polar surface,

[138]

[139]

and

Titan

, as a subsurface layer, possibly mixed with

ammonia

.

[140]

Jupiter’s moon

Europa

has surface characteristics which suggest a subsurface liquid water ocean.

[141]

Liquid water may also exist on Jupiter’s moon

Ganymede

as a layer sandwiched between high pressure ice and rock.

[142]

Water ice

Water is present as ice on:

South polar ice cap of Mars during Martian south summer 2000

  • Mars

    : under the regolith and at the poles.

    [143]

    [144]

  • Earth–Moon system: mainly as

    ice sheets

    on Earth and in Lunar craters and volcanic rocks

    [145]

    NASA reported the detection of water molecules by NASA’s Moon Mineralogy Mapper aboard the Indian Space Research Organization’s Chandrayaan-1 spacecraft in September 2009.

    [146]

  • Ceres

    [147]

    [148]

    [149]

  • Jupiter’s moons:

    Europa

    ‘s surface and also that of

    Ganymede

    [150]

    and

    Callisto

    [151]

    [152]

  • Saturn: in the

    planet’s ring system

    [153]

    and on the surface and mantle of

    Titan

    [154]

    and

    Enceladus

    [155]

  • Pluto

    Charon

    system

    [153]

  • Comets

    [156]

    [157]

    and other related

    Kuiper belt

    and

    Oort cloud

    objects

    [158]

And is also likely present on:

  • Mercury

    ‘s poles

    [159]

  • Tethys

    [160]

Exotic forms

Water and other

volatiles

probably comprise much of the internal structures of

Uranus

and

Neptune

and the water in the deeper layers may be in the form of

ionic water

in which the molecules break down into a soup of hydrogen and oxygen ions, and deeper still as

superionic water

in which the oxygen crystallises but the hydrogen ions float about freely within the oxygen lattice.

[161]

Water and planetary habitability

The existence of liquid water, and to a lesser extent its gaseous and solid forms, on Earth are vital to the existence of

life on Earth

as we know it. The Earth is located in the

habitable zone

of the

Solar System

; if it were slightly closer to or farther from the

Sun

(about 5%, or about 8 million kilometers), the conditions which allow the three forms to be present simultaneously would be far less likely to exist.

[162]

[163]

Earth’s

gravity

allows it to hold an

atmosphere

. Water vapor and carbon dioxide in the atmosphere provide a temperature buffer (

greenhouse effect

) which helps maintain a relatively steady surface temperature. If Earth were smaller, a thinner atmosphere would allow temperature extremes, thus preventing the accumulation of water except in

polar ice caps

(as on

Mars

).[

citation needed

]

The surface temperature of Earth has been relatively constant through

geologic time

despite varying levels of incoming solar radiation (

insolation

), indicating that a dynamic process governs Earth’s temperature via a combination of greenhouse gases and surface or atmospheric

albedo

. This proposal is known as the

Gaia hypothesis

.[

citation needed

]

The state of water on a planet depends on ambient pressure, which is determined by the planet’s gravity. If a planet is sufficiently massive, the water on it may be solid even at high temperatures, because of the high pressure caused by gravity, as it was observed on exoplanets

Gliese 436 b

[164]

and

GJ 1214 b

.

[165]

Law, politics, and crisis

An estimate of the proportion of people in developing countries with access to

potable water

1970–2000

Water politics

is politics affected by water and

water resources

. For this reason, water is a strategic resource in the globe and an important element in many political conflicts. It causes health impacts and damage to biodiversity.

Access to safe drinking water has improved over the last decades in almost every part of the world, but approximately one billion people still lack access to safe water and over 2.5 billion lack access to adequate

sanitation

.

[166]

However, some observers have estimated that by 2025 more than half of the

world population

will be facing water-based vulnerability.

[167]

A report, issued in November 2009, suggests that by 2030, in some developing regions of the world, water demand will exceed supply by 50%.

[168]

1.6 billion people have gained access to a safe water source since 1990.

[169]

The proportion of people in developing countries with access to safe water is calculated to have improved from 30% in 1970

[170]

to 71% in 1990, 79% in 2000 and 84% in 2004.

[166]

A 2006 United Nations report stated that “there is enough water for everyone”, but that access to it is hampered by mismanagement and corruption.

[171]

In addition, global initiatives to improve the efficiency of aid delivery, such as the

Paris Declaration on Aid Effectiveness

, have not been taken up by water sector donors as effectively as they have in education and health, potentially leaving multiple donors working on overlapping projects and recipient governments without empowerment to act.

[172]

The authors of the 2007

Comprehensive Assessment of Water Management in Agriculture

cited poor governance as one reason for some forms of water scarcity. Water governance is the set of formal and informal processes through which decisions related to water management are made. Good water governance is primarily about knowing what processes work best in a particular physical and socioeconomic context. Mistakes have sometimes been made by trying to apply ‘blueprints’ that work in the developed world to developing world locations and contexts. The Mekong river is one example; a review by the

International Water Management Institute

of policies in six countries that rely on the Mekong river for water found that thorough and transparent cost-benefit analyses and environmental impact assessments were rarely undertaken. They also discovered that Cambodia’s draft water law was much more complex than it needed to be.

[173]

The

UN World Water Development Report

(WWDR, 2003) from the

World Water Assessment Program

indicates that, in the next 20 years, the quantity of water available to everyone is predicted to decrease by 30%. 40% of the world’s inhabitants currently have insufficient fresh water for minimal

hygiene

. More than 2.2 million people died in 2000 from

waterborne diseases

(related to the consumption of contaminated water) or drought. In 2004, the UK charity

WaterAid

reported that a child dies every 15 seconds from easily preventable water-related diseases; often this means lack of

sewage

disposal.[

citation needed

]

Organizations concerned with water protection include the

International Water Association

(IWA),

WaterAid

,

Water 1st

, and the American Water Resources Association. The

International Water Management Institute

undertakes projects with the aim of using effective water management to reduce poverty. Water related conventions are

United Nations Convention to Combat Desertification

(UNCCD),

International Convention for the Prevention of Pollution from Ships

,

United Nations Convention on the Law of the Sea

and

Ramsar Convention

.

World Day for Water

takes place on 22 March

[174]

and

World Oceans Day

on 8 June.

[175]

In culture

Religion

People come to Inda Abba Hadera spring (

Inda Sillasie

,

Ethiopia

) to wash in holy water

Water is considered a purifier in most religions. Faiths that incorporate ritual washing (

ablution

) include

Christianity

,

Hinduism

,

Islam

,

Judaism

, the

Rastafari movement

,

Shinto

,

Taoism

, and

Wicca

. Immersion (or

aspersion

or

affusion

) of a person in water is a central

sacrament

of Christianity (where it is called

baptism

); it is also a part of the practice of other religions, including Islam (

Ghusl

), Judaism (

mikvah

) and

Sikhism

(

Amrit Sanskar

). In addition, a ritual bath in pure water is performed for the dead in many religions including Islam and Judaism. In Islam, the five daily prayers can be done in most cases after washing certain parts of the body using clean water (

wudu

), unless water is unavailable (see

Tayammum

). In Shinto, water is used in almost all rituals to cleanse a person or an area (e.g., in the ritual of

misogi

).

In Christianity,

holy water

is water that has been sanctified by a priest for the purpose of

baptism

, the

blessing

of persons, places, and objects, or as a means of repelling evil.

[176]

[177]

In

Zoroastrianism

, water (

āb

) is respected as the source of life.

[178]

Philosophy

The Ancient Greek philosopher

Empedocles

held that water is one of the four

classical elements

along with fire, earth and

air

, and was regarded as the

ylem

, or basic substance of the universe.

Thales

, who was portrayed by Aristotle as an astronomer and an engineer, theorized that the earth, which is denser than water, emerged from the water. Thales, a

monist

, believed further that all things are made from water. Plato believed the shape of water is an

icosahedron

which accounts for why it is able to flow easily compared to the cube-shaped earth.

[179]

In the theory of the

four bodily humors

, water was associated with

phlegm

, as being cold and moist. The

classical element of water

was also one of the

five elements

in traditional

Chinese philosophy

, along with

earth

,

fire

,

wood

, and

metal

.

Water is also taken as a role model in some parts of traditional and popular

Asian philosophy

.

James Legge

‘s 1891 translation of the

Dao De Jing

states, “The highest excellence is like (that of) water. The excellence of water appears in its benefiting all things, and in its occupying, without striving (to the contrary), the low place which all men dislike. Hence (its way) is near to (that of) the

Tao

” and “There is nothing in the world more soft and weak than water, and yet for attacking things that are firm and strong there is nothing that can take precedence of it—for there is nothing (so effectual) for which it can be changed.”

[180]

Guanzi

in the “Shui di” 水地 chapter further elaborates on the symbolism of water, proclaiming that “man is water” and attributing natural qualities of the people of different Chinese regions to the character of local water resources.

[181]

Art and activism

Painter and activist

Fredericka Foster

curated The Value of Water, at the

Cathedral of St. John the Divine

in New York City,

[182]

which anchored a year long initiative by the Cathedral on our dependence on water.

[183]

[184]

The largest exhibition to ever appear at the Cathedral,

[185]

it featured over forty artists, including

Jenny Holzer

,

Robert Longo

,

Mark Rothko

,

William Kentridge

,

April Gornik

,

Kiki Smith

,

Pat Steir

,

William Kentridge

,

Alice Dalton Brown

,

Teresita Fernandez

and

Bill Viola

.

[186]

[187]

The

Think About Water

water advocacy website was created by Foster to highlight artists who use water as their subject or medium.

Dihydrogen monoxide parody

Water’s technically correct but rarely used

chemical name

, “dihydrogen monoxide”, has been used in a series of

hoaxes

and

pranks

that mock

scientific illiteracy

. This began in 1983, when an

April Fools’ Day

article appeared in a newspaper in

Durand, Michigan

. The false story consisted of safety concerns about the substance.

[188]

See also

  • Outline of water

  • Water (data page)

    is a collection of the chemical and physical properties of water.

  • Aquaphobia

    (fear of water)

  • Mpemba effect

  • Dehydration

  • Oral rehydration therapy

  • Thirst

  • Water pinch analysis

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Further reading

  • Ball, Philip (2001). Life’s matrix : a biography of water (1st ed.). Farrar, Straus, and Giroux.

    ISBN

     

    9780520230088

    .

  • Debenedetti, PG., and HE Stanley, “Supercooled and Glassy Water”, Physics Today 56 (6), pp. 40–46 (2003).

    Downloadable PDF (1.9 MB)

  • Franks, Felix (2007). Water : a matrix of life (2nd ed.). Royal Society of Chemistry.

    ISBN

     

    9781847552341

    .

  • Gleick, PH., (editor), The World’s Water: The Biennial Report on Freshwater Resources. Island Press, Washington, D.C. (published every two years, beginning in 1998.)

    The World’s Water, Island Press

  • Jones, Oliver A.; Lester, John N.; Voulvoulis, Nick (2005). “Pharmaceuticals: a threat to drinking water?”. Trends in Biotechnology. 23 (4): 163–167.

    doi

    :

    10.1016/j.tibtech.2005.02.001

    .

    PMID

     

    15780706

    .

  • Journal of Contemporary Water Research & Education

  • Postel, S., Last Oasis: Facing Water Scarcity. W.W. Norton and Company, New York. 1992
  • Reisner, M., Cadillac Desert: The American West and Its Disappearing Water. Penguin Books, New York. 1986.
  • United Nations World Water Development Report

    . Produced every three years.

  • St. Fleur, Nicholas.

    The Water in Your Glass Might Be Older Than the Sun

    . “The water you drink is older than the planet you’re standing on.” The New York Times (15 April 2016)

External links

  • OECD Water statistics

  • The World’s Water Data Page

  • FAO Comprehensive Water Database, AQUASTAT

  • The Water Conflict Chronology: Water Conflict Database

  • Water science school

    (USGS)

  • Portal to The World Bank’s strategy, work and associated publications on water resources

  • America Water Resources Association

    Archived

    24 March 2018 at the

    Wayback Machine

  • Water on the web

  • Water structure and science

    Archived

    28 December 2014 at the

    Wayback Machine

  • Why water is one of the weirdest things in the universe

    BBC

    Ideas, Video, 3:16 minutes, 2019

  • The chemistry of water

    (NSF special report)

  • The International Association for the Properties of Water and Steam

  • H2O:The Molecule That Made Us

    , a 2020

    PBS

    documentary

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