Water is a transparent, tasteless, odorless, and nearly colorless
chemical substance that is the main constituent of Earth's streams,
lakes, and oceans, and the fluids of most living organisms. Its
chemical formula is H2O, meaning that each of its molecules contains
one oxygen and two hydrogen atoms that are connected by covalent
bonds. Strictly speaking, water refers to the liquid state of a
substance that prevails at standard ambient temperature and pressure;
but it often refers also to its solid state (ice) or its gaseous state
(steam or water vapor). It also occurs in nature as snow, glaciers,
ice packs and icebergs, clouds, fog, dew, aquifers, and atmospheric
Water covers 71% of the Earth's surface. It is vital for all known
forms of life. On Earth, 96.5% of the planet's crust water is found in
seas and oceans, 1.7% in groundwater, 1.7% in glaciers and the ice
caps of Antarctica and Greenland, a small fraction in other large
water bodies, 0.001% in the air as vapor, clouds (formed of ice and
liquid water suspended in air), and precipitation. Only 2.5% of
this water is freshwater, and 98.8% of that water is in ice (excepting
ice in clouds) and groundwater. Less than 0.3% of all freshwater is in
rivers, lakes, and the atmosphere, and an even smaller amount of the
Earth's freshwater (0.003%) is contained within biological bodies and
manufactured products. A greater quantity of water is found in the
Earth moves continually through the water cycle of
evaporation and transpiration (evapotranspiration), condensation,
precipitation, and runoff, usually reaching the sea.
transpiration contribute to the precipitation over land. Large amounts
of water are also chemically combined or adsorbed in hydrated
Safe drinking water is essential to humans and other lifeforms even
though it provides no calories or organic nutrients. 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. However, some observers have estimated that by 2025
more than half of the world population will be facing water-based
vulnerability. A report, issued in November 2009, suggests that by
2030, in some developing regions of the world, water demand will
exceed supply by 50%.
Water plays an important role in the world economy. Approximately 70%
of the freshwater used by humans goes to agriculture. Fishing in
salt and fresh water bodies is a major source of food for many parts
of the world. Much of long-distance trade of commodities (such as oil
and 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
Water is an excellent solvent for a wide variety of chemical
substances; as such it is widely used in industrial processes, and in
cooking and washing.
Water is also central to many sports and other
forms of entertainment, such as swimming, pleasure boating, boat
racing, surfing, sport fishing, and diving.
2 Chemical and physical properties
Taste and odor
2.3 Color and appearance
2.4 Polarity and hydrogen bonding
Electrical conductivity and electrolysis
2.6 Mechanical properties
3 On Earth
Fresh water storage
Sea water and tides
4 Effects on life
4.1 Aquatic life forms
5 Effects on human civilization
5.1 Health and pollution
5.2 Human uses
5.2.2 As a scientific standard
5.2.3 For drinking
5.2.6 Chemical uses
5.2.7 Heat exchange
5.2.8 Fire extinction
5.2.11 Industrial applications
5.2.13 Medical use
6 Distribution in nature
6.1 In the universe
6.1.2 Liquid water
6.1.4 Exotic forms
Water and habitable zone
7 Law, politics, and crisis
8 In culture
9 See also
11 Further reading
12 External links
The word "water" comes from
Old English "wæter", from Proto-Germanic
"*watar" (source also of
Old Saxon "watar",
Old Frisian "wetir", Dutch
Old High German
Old High German "wazzar", German "Wasser",
Old Norse "vatn",
Gothic "wato"), from Proto-Indoeuropean "*wod-or", suffixed form of
root "*wed-" ("water"; "wet").
Chemical and physical properties
Main article: Properties of water
Water (data page)
Water (data page) and
2O) 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. This allows it to be the
"solvent of life". It is the only common substance to exist as a
solid, liquid, and gas in normal terrestrial conditions.
Snowflakes by Wilson Bentley, 1902
Liquid water, showing droplets and air bubbles caused by the drops
Water is a liquid at the temperatures and pressures that are most
adequate for life. Specifically, at a standard pressure of 1 atm,
water is a liquid between 0 °C (32 °F) and 100 °C
(212 °F). Increasing the pressure slightly lowers the melting
point, which is about −5 °C at 600 atm and −22 °C at
2100 atm. This effect is relevant, for example, to ice skating, to the
buried lakes of Antarctica, and to the movement of glaciers. (At
pressures higher than 2100 atm the melting point rapidly increases
again, and ice takes several exotic forms that do not exist at lower
Increasing the pressure has a more dramatic effect on the boiling
point, that is about 374 °C at 220 atm. This effect is important
in, among other things, deep-sea hydrothermal vents and geysers,
pressure cooking, and steam engine design. At the top of Mount
Everest, where the atmospheric pressure is about 0.34 atm, water boils
at 68 °C (154 °F).
At very low pressures (below about 0.006 atm), water cannot exist in
the liquid state and passes directly from solid to gas by
sublimation—a phenomenon exploited in the freeze drying of food. At
very high pressures (above 221 atm), the liquid and gas states are no
longer distinguishable, a state called supercritical steam.
Water also differs from most liquids in that it becomes less dense as
it freezes. The maximum density of water in its liquid form (at
1 atm) is 1,000 kg/m3 (62.43 lb/cu ft); that
occurs at 3.98 °C (39.16 °F). The density of ice is
917 kg/m3 (57.25 lb/cu ft). Thus, water expands
9% in volume as it freezes, which accounts for the fact that ice
floats on liquid water.
The details of the exact chemical nature of liquid water are not well
understood; some theories suggest that water's unusual behaviour is as
a result of it having 2 liquid states.
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, and frogs are known to be able to smell it.
However, water from ordinary sources (including bottled mineral water)
usually has many dissolved substances, that may give it varying tastes
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.
Color and appearance
The apparent color of natural bodies of water (and swimming pools) is
often determined more by dissolved and suspended solids, or by
reflection of the sky, than by water itself.
Light in the visible electromagnetic spectrum can traverse a couple
meters of pure water (or ice) without significant absorption, so that
it looks transparent and colorless. Thus aquatic plants, algae,
and other photosynthetic organisms can live in water up to hundreds of
meters deep, because sunlight can reach them.
Water vapour is
essentially invisible as a gas.
Through a thickness of 10 meters or more, however, the intrinsic color
of water (or ice) is visibly turquoise (greenish blue), as its
absorption spectrum has a sharp minimum at the corresponding color of
light (1/227 m−1 at 418 nm). The color becomes increasingly
stronger and darker with increasing thickness. (Practically no
sunlight reaches the parts of the oceans below 1000 meters of depth.)
Infrared and ultraviolet light, on the other hand, is strongly
absorbed by water.
The refraction index of liquid water (1.333 at 20 °C) 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.
Polarity and hydrogen bonding
See also: Chemical bonding of H2O
Model of hydrogen bonds (1) between molecules of water.
Capillary action of water compared to mercury.
Impact from a water drop causes an upward "rebound" jet surrounded by
circular capillary waves.
Since the water molecule is not linear and the oxygen atom has a
higher electronegativity than hydrogen atoms, it is a polar molecule,
with an electrical dipole moment: the oxygen atom carries a slight
negative charge, whereas the hydrogen atoms are slightly positive.
Water is a good polar solvent, that dissolves many salts and
hydrophilic organic molecules such as sugars and simple alcohols such
as ethanol. Most acids dissolve in water to yield the corresponding
anions. Many substances in living organisms, such as proteins,
polysaccharides, are dissolved in water.
Water also dissolves many
gases, such as oxygen and carbon dioxide—the latter giving the fizz
of carbonated beverages, sparkling wines and beers.
On the other hand, 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,
Because of its polarity, a molecule of water in the liquid or solid
state can form up to four hydrogen bonds with neighboring molecules.
These bonds are the cause of water's high surface tension 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.
The hydrogen bonds are also the reason why the melting and boiling
points of water are much higher than those of other analogous
compounds like hydrogen sulfide (H
2S). 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 of moderate
strength, around 23 kJ/mol (compared to a covalent O-H bond at 492
kJ/mol). Of this, it is estimated that 90% of the hydrogen bond is
attributable to electrostatics, while the remaining 10% reflects
partial covalent character.
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
Liquid water can be assumed to be incompressible for most purposes:
its compressibility ranges from 4.4 to
6990510000000000000♠5.1×10−10 Pa−1 in ordinary
conditions. Even in oceans at 4 km depth, where the pressure
is 400 atm, water suffers only a 1.8% decrease in volume.
The viscosity of water is about 10−3 Pa·s or 0.01 poise at
20 °C, and the speed of sound in liquid water ranges between
1400 and 1540 m/s depending on temperature. Sound travels long
distances in water with little attenuation, especially at low
frequencies (roughly 0.03 dB/km for 1 kHz), a property that is
exploited by cetaceans and humans for communication and environment
Elements which are more electropositive than hydrogen such as lithium,
sodium, calcium, potassium and caesium displace hydrogen from water,
forming hydroxides and releasing hydrogen.
Water distribution on Earth
Water covers 71% of the Earth's surface; the oceans contain 96.5% of
the Earth's water. The Antarctic ice sheet, which contains 61% of all
fresh water on Earth, is visible at the bottom. Condensed atmospheric
water can be seen as clouds, contributing to the Earth's albedo.
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 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 1,338,000,000 km3
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.
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
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 following transfer processes:
evaporation from oceans and other water bodies into the air and
transpiration from land plants and animals into air.
precipitation, from water vapor condensing from the air and falling to
earth or ocean.
runoff from the land usually reaching the sea.
Most water vapor over the oceans returns to the oceans, but winds
carry water vapor over land at the same rate as runoff into the sea,
about 47 Tt per year. Over land, evaporation and transpiration
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.
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. 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
opportunity 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. It is when a river overflows its banks or flood comes from the
sea. A 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.
Fresh water storage
Bay of Fundy
Bay of Fundy at high tide (left) and low tide (right)
Some runoff water is trapped for periods of time, for example in
lakes. At high altitude, during winter, and in the far north and
south, snow collects in ice caps, snow pack and glaciers.
infiltrates the ground and goes into aquifers. This groundwater later
flows back to the surface in springs, or more spectacularly in hot
springs and geysers.
Groundwater is also extracted artificially in
wells. This water storage is important, since clean, fresh water is
essential to human and other land-based life. In many parts of the
world, it is in short supply.
Sea water and tides
Seawater and Tides
Sea water contains about 3.5% sodium chloride on average, plus smaller
amounts of other substances. The physical properties of sea water
differ from fresh water in some important respects. It freezes at a
lower temperature (about −1.9 °C) 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
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
An oasis is an isolated water source with vegetation in a desert.
Overview of photosynthesis and respiration.
Water (at right), together
with carbon dioxide (CO2), form oxygen and organic compounds (at
left), which can be respired to water and (CO2).
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.
Hydrogen is combined with CO2 (absorbed from air or water) to form
glucose and release oxygen. 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 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
Further information: Hydrobiology, Marine life, and Aquatic plant
Some of the biodiversity of a coral reef
Some marine diatoms – a key phytoplankton group
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 specialisation
for respiration in water.
Effects on human civilization
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. 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
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 that is not potable may be made potable by filtration or
distillation, or by a range of other methods.
Water that is not fit for drinking but is not harmful for 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 greywater, 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.
This natural resource is becoming scarcer in certain places, and its
availability is a major social and economic concern. Currently, about
a billion people around the world routinely drink unhealthy water.
Most countries accepted the goal of halving by 2015 the number of
people worldwide who do not have access to safe water and sanitation
during the 2003 G8 Evian summit. Even if this difficult goal is
met, it will still leave more than an estimated half a billion people
without access to safe drinking water and over a billion without
access to adequate sanitation. Poor water quality and bad sanitation
are deadly; some five million deaths a year are caused by polluted
drinking water. The
World Health Organization
World Health Organization estimates that safe
water could prevent 1.4 million child deaths from diarrhea each
Water, however, is not a finite resource (meaning the availability of
water is limited), but rather re-circulated as potable water in
precipitation in quantities many orders of magnitude higher than
human consumption. Therefore, it is the relatively small quantity of
water in reserve in the earth (about 1% of our drinking water
supply, which is replenished in aquifers around every
1 to 10 years), that is a non-renewable resource, and
it is, rather, the distribution of potable and irrigation water which
is scarce,[clarification needed] rather than the actual amount of it
that exists on the earth. Water-poor countries use importation of
goods as the primary method of importing water (to leave enough for
local human consumption),[further explanation needed] since the
manufacturing process[clarification needed] uses around 10 to 100
times products' masses in water.[clarification needed]
In the developing world, 90% of all wastewater still goes untreated
into local rivers and streams. 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. The strain not only affects
surface freshwater bodies like rivers and lakes, but it also degrades
Water distribution in subsurface drip irrigation
Irrigation of field crops
The most important use of water in agriculture is for irrigation,
which is a key component to produce enough food.
Irrigation takes up
to 90% of water withdrawn in some developing countries and
significant proportions in more economically developed countries (in
the United States, 30% of freshwater usage is for irrigation).
Fifty years ago, the common perception was that water was an infinite
resource. At the time, there were fewer than half the current number
of people on the planet. People were not as wealthy as today, consumed
fewer calories and ate less meat, so less water was needed to produce
their food. They required a third of the volume of water we presently
take from rivers. Today, the competition for the fixed amount of water
resources is much more intense, giving rise to the concept of peak
water. This is because there are now nearly seven billion people
on the planet, their consumption of water-thirsty meat and vegetables
is rising, and there is increasing competition for water from
industry, urbanisation and biofuel crops. In future, even more water
will be needed to produce food because the Earth's population is
forecast to rise to 9 billion by 2050.
An assessment of water management in agriculture was conducted in 2007
International Water Management Institute
International Water Management Institute in Sri Lanka to see if
the world had sufficient water to provide food for its growing
population. 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 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 industry and cities find ways to use
water more efficiently.
Water scarcity is also caused by production of cotton: 1 kg of
cotton—equivalent of a pair of jeans—requires 10.9 m3 water to
produce. While cotton accounts for 2.4% of world water use, the water
is consumed in regions which are already at a risk of water shortage.
Significant environmental damage has been caused, such as
disappearance of the Aral Sea.
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". 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—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).
Kelvin temperature scale
Kelvin temperature scale of the SI system is based on the triple
point of water, defined as exactly 273.16 K or 0.01 °C. 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) and melting point (set to
0 °C) of water.
Natural water consists mainly of the isotopes hydrogen-1 and
oxygen-16, but there is also a small quantity of heavier isotopes such
as hydrogen-2 (deuterium). The amount of deuterium oxides or heavy
water is very small, but it still affects the properties of water.
Water from rivers and lakes tends to contain less deuterium than
seawater. Therefore, standard water is defined in the Vienna Standard
Main article: Drinking water
A young girl drinking bottled water
Water availability: fraction of population using improved water
sources by country
The human body contains from 55% to 78% water, depending on body
size. To function properly, the body requires between one and
seven liters 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 most specialists agree that
approximately 2 liters (6 to 7 glasses) of water daily is the minimum
to maintain proper hydration. 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
For those who have healthy kidneys, it is rather difficult to drink
too much water, but (especially in warm humid weather and while
exercising) it is dangerous to drink too little. People can drink far
more water than necessary while exercising, however, putting them at
risk of water intoxication (hyperhydration), which can be
fatal. The popular claim that "a person should consume eight
glasses of water per day" seems to have no real basis in science.
Studies have shown that extra water intake, especially up to
500 ml at mealtime was conducive to weight
loss. Adequate fluid intake is helpful in
Hazard symbol for non-potable water
An original recommendation for water intake in 1945 by the
Nutrition Board of the
United States National Research Council
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." 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 for men and 2.7 liters of water total for women,
noting that water contained in food provided approximately 19% of
total water intake in the survey.
Specifically, pregnant and breastfeeding women need additional fluids
to stay hydrated. The
Institute of Medicine
Institute of Medicine (US) recommends that, on
average, men consume 3.0 liters and women 2.2 liters; pregnant women
should increase intake to 2.4 liters (10 cups) and breastfeeding women
should get 3 liters (12 cups), since an especially large amount of
fluid is lost during nursing. 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,
and/or harmful bacteria, such as Vibrio. Some solutes are acceptable
and even desirable for taste enhancement and to provide needed
The single largest (by volume) freshwater resource suitable for
Lake Baikal in Siberia.
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 personal water use
is due to showering, doing the laundry and dishwashing, reaching
hundreds of liters per day in developed countries.
Main article: Ship transport
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.
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. 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.
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
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.
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 but 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 reaction between steam and hot zirconium.
Water sport (recreation)
Grand Anse Beach, St. George's, Grenada, West Indies
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 life in 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.
A water-carrier in India, 1882. In many places where running water is
not available, water has to be transported by people.
A manual water pump in China
Water purification facility
Reverse osmosis (RO) desalination plant in Barcelona, Spain
The water industry provides drinking water and wastewater services
(including sewage treatment) to households and industry.
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.
require purification for human consumption. This may involve 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, sea
water is extensively used for flushing toilets citywide in order to
conserve fresh water 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
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.)
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
Three Gorges Dam is the largest hydro-electric power station.
Pressurized water is used in water blasting and water jet cutters.
Also, very 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.
Water can be used to cook foods such as noodles
Boiling, steaming, and simmering are popular cooking methods that
often require immersing food in water or its gaseous state, steam.
Water is also used for dishwashing.
Water also plays many critical
roles within the field of food science. It is important for a food
scientist to understand the roles that water plays within food
processing to ensure the success of their products.
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 is
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.
Solutes in water also affect water activity that affects many chemical
reactions and the growth of microbes in food.
Water activity can
be described as a ratio of the vapor pressure of water in a solution
to the vapor pressure of pure water. Solutes in water lower water
activity—this is important to know because most bacterial growth
ceases at low levels of water activity. 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.
classified as soft if it contains less than 100 mg/l (UK) or
less than 60 mg/l (US).
According to a report published by the
Water Footprint organization in
2010, a single kilogram of beef requires 15 thousand litres 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
Sterile water for injection
Water for injection is on the World Health Organization's list of
Distribution in nature
In the universe
Band 5 ALMA receiver is an instrument specifically designed to detect
water in the universe.
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
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
Water has been detected in interstellar clouds within our galaxy, the
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 is present as vapor in:
Atmosphere of the Sun: in detectable trace amounts
Atmosphere of Mercury: 3.4%, and large amounts of water in Mercury's
Atmosphere of Venus: 0.002%
Earth's atmosphere: ≈0.40% over full atmosphere, typically 1–4% at
surface; as well as that of the Moon in trace amounts
Atmosphere of Mars: 0.03%
Atmosphere of Ceres
Atmosphere of Jupiter: 0.0004% – in ices only; and that of its
Atmosphere of Saturn – in ices only; and that of its moons Titan
(stratospheric), Enceladus: 91% and Dione (exosphere)
Uranus – in trace amounts below 50 bar
Neptune – found in the deeper layers
Extrasolar planet atmospheres: including those of HD 189733 b and
HD 209458 b, Tau Boötis b, HAT-P-11b, XO-1b,
WASP-12b, WASP-17b, and WASP-19b.
Stellar atmospheres: not limited to cooler stars and even detected in
giant hot stars such as Betelgeuse, Mu Cephei,
Circumstellar disks: including those of more than half of T Tauri
stars such as AA Tauri as well as TW Hydrae, IRC
+10216 and APM 08279+5255,
VY Canis Majoris
VY Canis Majoris and S
Liquid water is present on Earth, covering 71% of its surface. Liquid
water is also occasionally present in small amounts on Mars.
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, and Titan,
as a subsurface layer, possibly mixed with ammonia. Jupiter's
moon Europa has surface characteristics which suggest a subsurface
liquid water ocean. Liquid water may also exist on Jupiter's moon
Ganymede as a layer sandwiched between high pressure ice and
Water is present as ice on:
Polar ice cap
Polar ice cap of
Mars during Martian South summer 2000
Mars: under the regolith and at the poles
Earth-Moon system: mainly as ice sheets on
Earth and in Lunar craters
and volcanic rocks
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.
Jupiter's moons: Europa's surface and also that of Ganymede
Saturn: in the planet's ring system and on the surface and mantle
of Titan and Enceladus
Comets and related (
Kuiper belt and
Oort cloud objects).
And may also be present on:
Water and other volatiles probably comprise much of the internal
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.
Water and habitable zone
Water distribution on Earth
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
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
5%, or about 8 million kilometers), the conditions which allow the
three forms to be present simultaneously would be far less likely to
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
Earth were smaller, a thinner atmosphere would allow
temperature extremes, thus preventing the accumulation of water except
in polar ice caps (as on Mars).
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.
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 and GJ 1214 b.
Law, politics, and crisis
Water right, and
An estimate of the share 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.
1.6 billion people have gained access to a safe water source since
1990. The proportion of people in developing countries with
access to safe water is calculated to have improved from 30% in
1970 to 71% in 1990, 79% in 2000 and 84% in 2004. This trend is
projected to continue. To halve, by 2015, the proportion of people
without sustainable access to safe drinking water is one of the
Millennium Development Goals. This goal is projected to be reached.
A 2006 United Nations report stated that "there is enough water for
everyone", but that access to it is hampered by mismanagement and
corruption. 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.
The authors of the 2007 Comprehensive Assessment of
in Agriculture cited poor governance as one reason for some forms of
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.
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; see toilet.
Organizations concerned with water protection include the
International Water Association (IWA), WaterAid,
Water 1st, and the
Water Resources Association. The International Water
Management Institute undertakes projects with the aim of using
effective water management to reduce poverty.
conventions are United Nations Convention to Combat Desertification
(UNCCD), International Convention for the Prevention of Pollution from
United Nations Convention on the Law of the Sea
United Nations Convention on the Law of the Sea and Ramsar
World Day for Water
World Day for Water takes place on 22 March and World
Ocean Day on 8 June.
Water and religion
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
Judaism (mikvah) and
Sikhism (Amrit Sanskar). In addition, a ritual
bath in pure water is performed for the dead in many religions
Islam and Judaism. In Islam, the five daily prayers can be
done in most cases after completing 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.
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
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." Guanzi in "Shui di" 水地 chapter further
elaborates on 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.
Sustainable development portal
Main article: Outline of water
The water (data page) is a collection of the chemical and physical
properties of water.
Aquaphobia (fear of water)
Dihydrogen monoxide hoax
Oral rehydration therapy
Water Pasteurization Indicator
Water pinch analysis
^ "CIA – The world factbook". Central Intelligence Agency. Retrieved
20 December 2008.
^ a b c Gleick, P.H., ed. (1993).
Water in Crisis: A Guide to the
Freshwater Resources. Oxford University Press. p. 13,
Table 2.1 "
Water reserves on the earth". Archived from the original on
8 April 2013.
Vapor in the
Special Report, [AGU], December
1995 (linked 4/2007). Vital
Water UNEP. Archived 8 July 2009 at the
^ Crocket, Christopher (5 September 2015). "Quest to trace origin of
Earth's water is 'a complete mess'". Science News. Retrieved 1 October
^ a b "MDG Report 2008" (PDF). Retrieved 25 July 2010.
^ Kulshreshtha, S.N (1998). "A Global Outlook for
Water Resources to
the Year 2025".
Water Resources Management. 12 (3): 167–184.
^ "Charting Our
Water Future: Economic frameworks to inform
decision-making" (PDF). Archived from the original (PDF) on 5 July
2010. Retrieved 25 July 2010.
^ Baroni, L.; Cenci, L.; Tettamanti, M.; Berati, M. (2007).
"Evaluating the environmental impact of various dietary patterns
combined with different food production systems". European Journal of
Clinical Nutrition. 61 (2): 279–286. doi:10.1038/sj.ejcn.1602522.
Water (v.)". www.etymonline.com. Online Etymology Dictionary.
Retrieved 20 May 2017.
^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the
Elements (2nd ed.). Butterworth-Heinemann. p. 620.
^ "Water, the Universal Solvent". USGS.
^ Reece, Jane B. (31 October 2013). Campbell
Biology (10 ed.).
Pearson. p. 48. ISBN 9780321775658.
^ Reece, Jane B. (31 October 2013). Campbell
Biology (10 ed.).
Pearson. p. 44. ISBN 9780321775658.
^ a b "Water: Water—an enduring mystery". Nature. Retrieved 15
^ Kotz, J. C., Treichel, P., & Weaver, G. C. (2005). Chemistry
& Chemical Reactivity. Thomson Brooks/Cole.
ISBN 0-534-39597-X. CS1 maint: Multiple names: authors list
^ Ben-Naim, Ariel; Ben-Naim, Roberta; et al. (2011). Alice's
Adventures in Water-land. Singapore. doi:10.1142/8068.
^ Maestro, L.m.; Marqués, M.i.; Camarillo, E.; Jaque, D.; Solé, J.
García; Gonzalo, J.a.; Jaque, F.; Valle, Juan C. Del; Mallamace, F.
(1 January 2016). "On the existence of two states in liquid water:
impact on biological and nanoscopic systems". International Journal of
Nanotechnology. 13 (8–9): 667–677. Bibcode:2016IJNT...13..667M.
^ Mallamace, Francesco; Corsaro, Carmelo; Stanley, H. Eugene (18
December 2012). "A singular thermodynamically consistent temperature
at the origin of the anomalous behavior of liquid water". Scientific
Reports. 2 (1): 993. Bibcode:2012NatSR...2E.993M.
^ Perakis, Fivos; Amann-Winkel, Katrin; Lehmkühler, Felix; Sprung,
Michael; Mariedahl, Daniel; Sellberg, Jonas A.; Pathak, Harshad;
Späh, Alexander; Cavalca, Filippo; Ricci, Alessandro; Jain, Avni;
Massani, Bernhard; Aubree, Flora; Benmore, Chris J.; Loerting, Thomas;
Grübel, Gerhard; Pettersson, Lars G. M.; Nilsson, Anders (26 June
2017). "Diffusive dynamics during the high-to-low density transition
in amorphous ice". Proceedings of the National Academy of Sciences of
the United States of America. 13 (8–9): 667–677.
doi:10.1073/pnas.1705303114. PMC 5547632 .
^ Edmund T. Rolls (2005), "Emotion Explained". Oxford University
Press, Medical. ISBN 0198570031, 9780198570035.
^ R. Llinas, W. Precht (2012), "Frog Neurobiology: A Handbook".
Springer Science & Business Media. ISBN 3642663168,
^ Candau, Joël (2004). "The Olfactory Experience: constants and
Water Science and Technology. 49 (9):
^ Braun, Charles L.; Sergei N. Smirnov (1993). "Why is water blue?".
J. Chem. Educ. 70 (8): 612. Bibcode:1993JChEd..70..612B.
^ Campbell, Neil A.; Brad Williamson; Robin J. Heyden (2006). Biology:
Exploring Life. Boston, Massachusetts: Pearson Prentice Hall.
^ Capillary Action – Liquid, Water, Force, and Surface – JRank
Articles. Science.jrank.org. Retrieved on 28 September 2015.
^ Isaacs, E.D; Shukla, A; Platzman, P.M; Hamann, D.R; Barbiellini, B;
Tulk, C.A (1 March 2000). "Compton scattering evidence for covalency
of the hydrogen bond in ice". Journal of Physics and Chemistry of
Solids. 61 (3): 403–406. Bibcode:2000JPCS...61..403I.
^ Ball, Philip (14 September 2007). "Burning water and other myths".
Nature News. Retrieved 14 September 2007.
^ Fine, R.A. & Millero, F.J. (1973). "Compressibility of water as
a function of temperature and pressure". Journal of Chemical Physics.
59 (10): 5529. Bibcode:1973JChPh..59.5529F.
^ Nave, R. "Bulk Elastic Properties". HyperPhysics. Georgia State
University. Retrieved 26 October 2007.
^ UK National Physical Laboratory, Calculation of absorption of sound
in seawater. Online site, last accessed on 28 September 2016.
^ Gleick, P.H., ed. (1993).
Water in Crisis: A Guide to the World's
Freshwater Resources. Oxford University Press. p. 15, Table 2.3.
Archived from the original on 8 April 2013.
^ Ben-Naim, A. & Ben-Naim, R., P.H. (2011). Alice's Adventures in
Water-land. World Scientific Publishing. p. 31. doi:10.1142/8068.
ISBN 978-981-4338-96-7. CS1 maint: Multiple names: authors
^ "G8 "Action plan" decided upon at the 2003 Evian summit". G8.fr. 2
June 2003. Archived from the original on 8 June 2003. Retrieved 25
^ "World Health Organization. Safe
Water and Global Health". Who.int.
25 June 2008. Retrieved 25 July 2010.
^ Hoekstra, Arjen Y. (19 June 2013). The
Water Footprint of Modern
Consumer Society. Routledge. ISBN 1136457046.
UNEP International Environment (2002). Environmentally Sound
Stormwater Management: An International
Source Book. IWA Publishing. ISBN 1-84339-008-6.
^ Ravindranath, Nijavalli H.; Jayant A. Sathaye (2002).
and Developing Countries. Springer. ISBN 1-4020-0104-5.
Water Facts & Trends". Archived from the original on 1
March 2012. Retrieved 25 July 2010.
^ a b
Water Use in the United States, National Atlas.gov Archived 14
August 2009 at the Wayback Machine.
^ Gleick, P.H.; Palaniappan, M. (2010). "Peak Water" (PDF).
Proceedings of the National Academy of Sciences. National Academy of
Science. 107 (125): 11155–11162. Bibcode:2010PNAS..10711155G.
doi:10.1073/pnas.1004812107. Retrieved 11 October 2011.
^ United Nations Press Release POP/952 (13 March 2007). World
population will increase by 2.5 billion by 2050
^ Molden, D. (Ed).
Water for food,
Water for life: A Comprehensive
Water Management in Agriculture. Earthscan/IWMI, 2007.
^ Chartres, C. and Varma, S. (2010) Out of water. From Abundance to
Scarcity and How to Solve the World's
Water Problems. FT Press (US).
^ Décret relatif aux poids et aux mesures. 18 germinal an 3 (7 April
1795). Decree relating to the weights and measurements (in French).
^ here L'Histoire Du Mètre, La Détermination De L'Unité De Poids.
^ Re: What percentage of the human body is composed of water? Jeffrey
Utz, M.D., The MadSci Network
Water Living". BBC. Archived from the original on 1 January
2007. Retrieved 1 February 2007.
^ Rhoades RA, Tanner GA (2003). Medical Physiology (2nd ed.).
Baltimore: Lippincott Williams & Wilkins. ISBN 0-7817-1936-4.
^ Noakes TD; Goodwin N; Rayner BL; et al. (1985). "
a possible complication during endurance exercise". Med Sci Sports
Exerc. 17 (3): 370–375. doi:10.1249/00005768-198506000-00012.
^ Noakes TD, Goodwin N, Rayner BL, Branken T, Taylor RK (2005). "Water
intoxication: a possible complication during endurance exercise,
Wilderness Environ Med. 16 (4): 221–227.
^ ""Drink at least eight glasses of water a day." Really? Is there
scientific evidence for "8 × 8"?". Archived from the original on 20
April 2010. Retrieved 3 March 2016.
^ Stookey JD, Constant F, Popkin BM, Gardner CD (November 2008).
Drinking water is associated with weight loss in overweight dieting
women independent of diet and activity". Obesity. 16 (11):
2481–2488. doi:10.1038/oby.2008.409. PMID 18787524.
^ "Drink water to curb weight gain? Clinical trial confirms
effectiveness of simple appetite control method".
www.sciencedaily.com. 23 August 2010. Retrieved 14 May 2017.
^ Dubnov-Raz G, Constantini NW, Yariv H, Nice S, Shapira N (October
2011). "Influence of water drinking on resting energy expenditure in
overweight children". International Journal of Obesity. 35 (10):
1295–1300. doi:10.1038/ijo.2011.130. PMID 21750519.
^ Dennis EA; Dengo AL; Comber DL; et al. (February 2010). "Water
consumption increases weight loss during a hypocaloric diet
intervention in middle-aged and older adults". Obesity. 18 (2):
300–307. doi:10.1038/oby.2009.235. PMC 2859815 .
^ Vij VA, Joshi AS (September 2013). "Effect of 'water induced
thermogenesis' on body weight, body mass index and body composition of
overweight subjects". Journal of Clinical and Diagnostic Research. 7
(9): 1894–1896. doi:10.7860/JCDR/2013/5862.3344.
PMC 3809630 . PMID 24179891.
^ Muckelbauer R, Sarganas G, Grüneis A, Müller-Nordhorn J (August
2013). "Association between water consumption and body weight
outcomes: a systematic review". The American Journal of Clinical
Nutrition. 98 (2): 282–299. doi:10.3945/ajcn.112.055061.
^ Water, Constipation, Dehydration, and Other Fluids.
Sciencedaily.com. Retrieved on 28 September 2015.
Food and Nutrition Board, National Academy of Sciences. Recommended
Dietary Allowances. National Research Council, Reprint and Circular
Series, No. 122. 1945. pp. 3–18.
Water Dietary Reference Intakes for Water, Potassium, Sodium,
Chloride, and Sulfate The National Academies Press.
^ "Water: How much should you drink every day?". Mayoclinic.com.
Retrieved 25 July 2010.
^ Conquering Chemistry 4th Ed. Published 2008
^ Maton, Anthea; Jean Hopkins; Charles William McLaughlin; Susan
Johnson; Maryanna Quon Warner; David LaHart; Jill D. Wright (1993).
Biology and Health. Englewood Cliffs, New Jersey: Prentice Hall.
ISBN 0-13-981176-1. OCLC 32308337.
^ Unesco (2006). Water: a shared responsibility. Berghahn Books.
p. 125. ISBN 1-84545-177-5.
^ "The reaction network in propane oxidation over phase-pure MoVTeNb
M1 oxide catalysts" (PDF). Journal of Catalysis. 311: 369–385. 2014.
^ "Surface chemistry of phase-pure M1 MoVTeNb oxide during operation
in selective oxidation of propane to acrylic acid" (PDF). Journal of
Catalysis. 285: 48–60. 2012. doi:10.1016/j.jcat.2011.09.012.
^ Kinetic studies of propane oxidation on Mo and V based mixed oxide
catalysts (PDF). 2011.
^ "Multifunctionality of Crystalline MoV(TeNb) M1
Oxide Catalysts in
Oxidation of Propane and Benzyl Alcohol". ACS Catalysis. 3
(6): 1103–1113. 2013. doi:10.1021/cs400010q.
^ Duff, Sister Loretto Basil (1916). A Course in Household Arts: Part
I. Whitcomb & Barrows.
^ a b Vaclavik, Vickie A. & Christian, Elizabeth W (2007).
Food Science. Springer. ISBN 0-387-69939-2.
^ a b DeMan, John M (1999). Principles of
Food Chemistry. Springer.
^ "Map showing the rate of hardness in mg/l as
Calcium carbonate in
England and Wales" (PDF). DEFRA/ Drinking
Water hardness". US Geological Service. 8 April 2014.
^ M.M. Mekonnen; A.Y. Hoekstra (December 2010). "The green, blue and
grey water footprint of farm animals and animal products, Value of
Water Research Report Series No. 48 – Volume 1: Main report" (PDF).
The green, blue and grey water footprint of farm animals and animal
products, Value of
Water Research Report Series No. 48 – Volume 1:
UNESCO – IHE Institute for
Water Education. Retrieved
30 January 2014.
^ "WHO Model List of EssentialMedicines" (PDF). World Health
Organization. October 2013. Retrieved 22 April 2014.
^ "ALMA Greatly Improves Capacity to Search for
Water in Universe".
Retrieved 20 July 2015.
^ Melnick, Gary,
Harvard-Smithsonian Center for Astrophysics
Harvard-Smithsonian Center for Astrophysics and
Johns Hopkins University
Johns Hopkins University quoted in: "Discover of Water
Vapor Near Orion Nebula Suggests Possible Origin of H20 in Solar
System (sic)". The Harvard University Gazette. 23 April 1998. Archived
from the original on 16 January 2000. "Space Cloud Holds Enough
Water to Fill Earth's Oceans 1 Million Times". Headlines@Hopkins, JHU.
9 April 1998. "Water,
Water Everywhere: Radio telescope finds
water is common in universe". The Harvard University Gazette. 25
February 1999. (archive link)
^ a b Clavin, Whitney; Buis, Alan (22 July 2011). "Astronomers Find
Largest, Most Distant Reservoir of Water". NASA. Retrieved 25 July
^ a b Staff (22 July 2011). "Astronomers Find Largest, Oldest Mass of
Water in Universe". Space.com. Retrieved 23 July 2011.
^ Bova, Ben (13 October 2009). Faint Echoes, Distant Stars: The
Science and Politics of Finding
Life Beyond Earth. Zondervan.
^ Solanki, S. K.; Livingston, W.; Ayres, T. (1994). "New Light on the
Heart of Darkness of the Solar Chromosphere". Science. 263 (5143):
64–66. Bibcode:1994Sci...263...64S. doi:10.1126/science.263.5143.64.
^ "MESSENGER Scientists 'Astonished' to Find
Water in Mercury's Thin
Atmosphere". Planetary Society. 3 July 2008. Archived from the
original on 17 January 2010. Retrieved 5 July 2008.
^ Bertaux, Jean-Loup; Vandaele, Ann-Carine; Korablev, Oleg; Villard,
E.; Fedorova, A.; Fussen, D.; Quémerais, E.; Belyaev, D.; et al.
(2007). "A warm layer in Venus' cryosphere and high-altitude
measurements of HF, HCl, H2O and HDO". Nature. 450 (7170): 646–649.
^ Sridharan, R.; Ahmed, S.M.; Dasa, Tirtha Pratim; Sreelathaa, P.;
Pradeepkumara, P.; Naika, Neha; Supriya, Gogulapati (2010). "'Direct'
evidence for water (H2O) in the sunlit lunar ambience from CHACE on
MIP of Chandrayaan I". Planetary and Space Science. 58 (6): 947.
^ Rapp, Donald (28 November 2012). Use of Extraterrestrial Resources
for Human Space Missions to Moon or Mars. Springer. p. 78.
^ Küppers, M.; O'Rourke, L.; Bockelée-Morvan, D.; Zakharov, V.; Lee,
S.; Von Allmen, P.; Carry, B.; Teyssier, D.; Marston, A.; Müller, T.;
Crovisier, J.; Barucci, M. A.; Moreno, R. (23 January 2014).
"Localized sources of water vapour on the dwarf planet (1) Ceres".
Nature. 505 (7484): 525–527. Bibcode:2014Natur.505..525K.
doi:10.1038/nature12918. PMID 24451541.
^ Atreya, Sushil K.; Wong, Ah-San (2005). "Coupled Clouds and
Chemistry of the Giant Planets — A Case for Multiprobes" (PDF).
Space Science Reviews. 116: 121–136. Bibcode:2005SSRv..116..121A.
^ Cook, Jia-Rui C.; Gutro, Rob; Brown, Dwayne; Harrington, J.D.; Fohn,
Joe (12 December 2013). "Hubble Sees Evidence of
Jupiter Moon". NASA. Retrieved 12 December 2013.
^ Hansen; C. J.; et al. (2006). "Enceladus'
Science. 311 (5766): 1422–1425. Bibcode:2006Sci...311.1422H.
doi:10.1126/science.1121254. PMID 16527971.
^ Hubbard, W. B. (1997). "Neptune's Deep Chemistry". Science. 275
(5304): 1279–1280. doi:10.1126/science.275.5304.1279.
Water Found on Distant Planet 12 July 2007 By Laura Blue, Time
Water Found in Extrasolar Planet's
Atmosphere – Space.com
^ Near-IR Direct Detection of
Vapor in Tau Boo b: Alexandra C.
Lockwood, John A. Johnson, Chad F. Bender, John S. Carr, Travis
Barman, Alexander J.W. Richert, Geoffrey A. Blake
^ Clavin, Whitney; Chou, Felicia; Weaver, Donna; Villard; Johnson,
Michele (24 September 2014). "
NASA Telescopes Find Clear Skies and
Vapor on Exoplanet". NASA. Retrieved 24 September 2014.
^ a b c Arnold Hanslmeier (29 September 2010).
Water in the Universe.
Springer Science & Business Media. pp. 159–.
^ "Hubble Traces Subtle Signals of
Water on Hazy Worlds". NASA. 3
December 2013. Retrieved 4 December 2013.
^ a b Andersson, Jonas (June 2012).
Water in stellar atmospheres "Is a
novel picture required to explain the atmospheric behavior of water in
red giant stars?" Lund Observatory, Lund University, Sweden
^ Herschel Finds Oceans of
Water in Disk of Nearby Star. Nasa.gov (20
October 2011). Retrieved on 28 September 2015.
^ Herschel Finds Oceans of
Water in Disk of Nearby Star Archived 4
June 2012 at the Wayback Machine.
^ Lloyd, Robin. "
Water Vapor, Possible Comets, Found Orbiting Star",
11 July 2001, Space.com. Retrieved 15 December 2006. Archived 23 May
2009 at the Wayback Machine.
^ Platt, Jane; Bell, Brian (3 April 2014). "
NASA Space Assets Detect
Ocean inside Saturn Moon". NASA. Retrieved 3 April 2014.
^ Iess, L.; Stevenson, D.J.; Parisi, M.; Hemingway, D.; Jacobson,
R.A.; Lunine, J.I.; Nimmo, F.; Armstrong, J.w.; Asmar, S.w.; Ducci,
M.; Tortora, P. (4 April 2014). "The
Gravity Field and Interior
Structure of Enceladus". Science. 344 (6179): 78–80.
PMID 24700854. Retrieved 3 April 2014.
^ Dunaeva, A. N.; Kronrod, V. A.; Kuskov, O. L. "Numerical Models of
Titan's Interior with Subsurface Ocean". 44th Lunar and Planetary
Science Conference, held March 18–22, 2013 in The Woodlands, Texas.
LPI Contribution No. 1719 (PDF). p. 2454.
^ Tritt, Charles S. (2002). "Possibility of
Life on Europa". Milwaukee
School of Engineering. Archived from the original on 9 June 2007.
Retrieved 10 August 2007.
^ Dunham, Will. (3 May 2014) Jupiter's moon Ganymede may have 'club
sandwich' layers of ocean Reuters. In.reuters.com. Retrieved on 28
^ Versteckt in Glasperlen: Auf dem Mond gibt es Wasser –
Der Spiegel – Nachrichten
Water Molecules Found on the Moon Archived 27 September 2009 at the
Wayback Machine., NASA, 24 September 2009
^ a b Sparrow, Giles (2006). The Solar System. Thunder Bay Press.
^ NASA, "MESSENGER Finds New Evidence for
Ice at Mercury's
Poles", 29 November 2012.
^ Weird water lurking inside giant planets, New Scientist, 1 September
2010, Magazine issue 2776.
^ Ehlers, E.; Krafft, T, eds. (2001). "J. C. I. Dooge. "Integrated
Water Resources"". Understanding the
compartments, processes, and interactions. Springer.
^ "Habitable Zone". The Encyclopedia of Astrobiology, Astronomy and
^ Shiga, David (6 May 2007). "Strange alien world made of "hot ice"".
New Scientist. Archived from the original on 6 July 2008. Retrieved 28
^ Aguilar, David A. (16 December 2009). "Astronomers Find Super-Earth
Using Amateur, Off-the-Shelf Technology". Harvard-Smithsonian Center
for Astrophysics. Retrieved 28 March 2010.
Millennium Development Goals
Millennium Development Goals Report, United Nations, 2008
^ Lomborg, Björn (2001). The Skeptical Environmentalist (PDF).
Cambridge University Press. p. 22. ISBN 0-521-01068-3.
Archived from the original (PDF) on 25 July 2013.
^ UNESCO, (2006), Water, a shared responsibility. The United Nations
Water Development Report 2.
^ Welle, Katharina; Evans, Barbara; Tucker, Josephine and Nicol, Alan
(2008) Is water lagging behind on Aid Effectiveness?
^ "Search Results".
International Water Management Institute
International Water Management Institute (IWMI).
Retrieved 3 March 2016.
^ Chambers's encyclopædia, Lippincott & Co (1870). p. 394.
^ Altman, Nathaniel (2002) Sacred water: the spiritual source of life.
pp. 130–133. ISBN 1-58768-013-0.
^ Lindberg, D. (2008). The beginnings of western science: The European
scientific tradition in philosophical, religious, and institutional
context, prehistory to A.D. 1450. (2nd ed.). Chicago: University of
^ "Internet Sacred Text Archive Home". Sacred-texts.com. Retrieved 25
^ Guanzi : Shui Di – Chinese Text Project. Ctext.org. Retrieved
on 28 September 2015.
Debenedetti, PG., and HE Stanley, "Supercooled and Glassy Water",
Physics Today 56 (6), pp. 40–46 (2003). Downloadable PDF (1.9
Franks, F (Ed), Water, A comprehensive treatise, Plenum Press, New
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.
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
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)
Find more aboutwaterat's sister projects
Definitions from Wiktionary
Media from Wikimedia Commons
News from Wikinews
Quotations from Wikiquote
Texts from Wikisource
Textbooks from Wikibooks
Learning resources from Wikiversity
Water Data Page
Water Database, AQUASTAT
Water Conflict Chronology:
Water Conflict Database
US Geological Survey
Water for Schools information
Portal to The World Bank's strategy, work and associated publications
on water resources
Water Resources Association
Water structure and science
Essential fatty acids
"Minerals" (Chemical elements)
Pollution / quality
Ambient standards (USA)
Clean Air Act (USA)
Fossil fuels (peak oil)
Non-timber forest products
Types / location
storage and recovery
Earth Overshoot Day
Renewable / Non-renewable
Agriculture and agronomy
Molecules detected in outer space
Magnesium monohydride cation
Hydrogen cyanide (HCN)
Hydrogen isocyanide (HNC)
Protonated molecular hydrogen
Protonated carbon dioxide
Protonated hydrogen cyanide
Buckminsterfullerene (C60 fullerene, buckyball)
Ethyl methyl ether
Atomic and molecular astrophysics
Diffuse interstellar band
Earliest known life forms
Extraterrestrial liquid water
Helium hydride ion
Iron–sulfur world theory
Molecules in stars
Nexus for Exoplanet System Science
PAH world hypothesis
Polycyclic aromatic hydrocarbon
Polycyclic aromatic hydrocarbon (PAH)
RNA world hypothesis