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{{two other uses|the chemical substance|a discussion of its properties|water (molecule)}}


[[Image:Water droplet blue bg05.jpg||right|thumb|280px|Impact from a water drop causes an upward "rebound" jet surrounded by circular [[capillary wave]]s.]]
'''Water''' is a common [[chemical substance]] that is essential to all known forms of [[life]].<ref>http://pubs.acs.org/cgi-bin/abstract.cgi/bichaw/1997/36/i43/abs/bi971323j.html</ref>
In typical usage, ''water'' refers only to its [[liquid]] form or [[States of matter|state]], but the substance also has a [[solid]] state, ''[[ice]]'', and a [[gaseous]] state, ''[[water vapor]]''. About 1,460 [[Tonne#Multiples|teratonnes]] (Tt) of water cover 71% of [[Earth]]'s surface, mostly in oceans and other large water bodies, with 1.6% of water below ground in [[aquifer]]s and 0.001% in the [[atmosphere|air]] as [[vapor]], [[cloud]]s (formed of solid and liquid water particles suspended in air), and [[precipitation (meteorology)|precipitation]].<ref>
[http://www.agu.org/sci_soc/mockler.html Water Vapor in the Climate System], Special Report, [AGU], December 1995 (linked 4/2007). [http://www.unep.org/vitalwater/01.htm Vital Water] [[UNEP]].</ref> Some of the Earth's water is a part of man-made and natural objects near the earth's surface such as water towers, and animal and plant bodies, manufactured products, and food stores.


Water is your urine evaporated and cleaned. Also known as H2O
[[Seawater|Saltwater]] [[ocean]]s hold 97.0% of surface water, [[glacier]]s and polar [[ice cap]]s 2.4%, and other land surface water such as [[river]]s and [[lake]]s 0.6%. Water in these forms moves perpetually through the ''[[water cycle]]'' of [[evaporation]] and [[transpiration]], [[precipitation (meteorology)|precipitation]], and [[runoff (water)|runoff]] usually reaching the [[sea]]. Winds carry water vapor over land at the same rate as runoff into the sea, about 36 [[Tonne#Multiples|Tt]] per year. Over land, evaporation and transpiration contribute another 71 Tt per year to the precipitation of 107 Tt per year over land. Some water is trapped for periods in ice caps, glaciers, aquifers, or in lakes, for varying periods, sometimes providing fresh water for life on land. Clean, fresh water is essential to [[human]] and other life. In many parts of the world, it is in short supply. Many very important chemical substances, such as [[salt]]s, [[sugar]]s, [[acid]]s, [[alkali]]s, some [[gas]]es (especially [[oxygen]]), and many [[organic molecule]]s [[solvent|dissolve]] in water.

Outside of our planet, a significant quantity is thought to exist underground on the planet [[Mars]], on the moons [[Europa (moon)|Europa]] and [[Enceladus (moon)|Enceladus]], and on the [[exoplanet]]s known as [[HD 189733 b]]<ref>[http://www.time.com/time/health/article/0,8599,1642811,00.html Water Found on Distant Planet July 12, 2007 By LAURA BLUE [[TIME]]</ref> and [[HD 209458 b]].<ref name="Space.com water"> [http://www.space.com/scienceastronomy/070410_water_exoplanet.html Water Found in Extrasolar Planet's Atmosphere] - Space.com </ref>

[[Image:The Earth seen from Apollo 17.jpg|right|thumb|150px|Water covers 71% the [[Earth]]'s surface; the [[ocean]]s contain 97.2% of Earth's water. The [[Antarctic ice sheet]], which contains 90% of all fresh water on Earth, is visible at the bottom. Condensed atmospheric water can be seen as [[cloud]]s, contributing to the earth's [[albedo]].]]
<!--[[Image:Trilliumlake.jpg|right|280px|thumb|Trillium Lake in the [[Mount Hood National Forest|Mt. Hood National Forest]]]]-->

== Chemical and physical properties ==
{| align="right" border="1" cellspacing="0" cellpadding="3" style="margin: 0 0 0 0.5em; background: #FFFFFF; border-collapse: collapse; border-color: #C0C090;"
! {{chembox header}} | <big>[[Water (molecule)|Water]]</big>
|-
| align="center" colspan="2" bgcolor="#ffffff" | [[Image:Water molecule dimensions.svg|135px|The dimensions and geometric structure of a water molecule]][[Image:Water molecule.svg|110px|This space-filled model shows the molecular structure of water.]]
Water is the base of human life, and<br>an abundant [[chemical compound|compound]] on the earth's surface.
|-
! {{chembox header}} | Information and properties
|-
| [[IUPAC nomenclature|Systematic name]]
| water
|-
| Alternative names
| aqua, [[dihydrogen monoxide]], <br>hydrogen hydroxide, ([[wikt:wikisaurus:water|more]])
|-
| [[Molecular formula]]
| H<sub>2</sub>O
|-
| [[Molar mass]]
| 18.0153 g/mol
|-
| [[Density]] and [[Phase (matter)|phase]]
| 0.998 g/cm³ <small>(liquid at 20 °C)</small><br> 0.92 g/cm³ <small>(solid)</small>
|-
| [[Melting point]]
| 0 [[Celsius|°C]] (273.15 [[kelvin|K]]) (32 [[Fahrenheit|&deg;F]])
|-
| [[Boiling point]]
| 100 °C (373.15 K) (212 &deg;F)
|-
| [[Specific heat capacity]]
| 4.184 J/(g•K) <small>(liquid at 20 °C)</small>
|-
! {{chembox header}} | [[Water (data page)|Supplementary data page]]
|-
| align="center" cellspacing="3" style="border: 1px solid #C0C090; background-color: #F8EABA; margin-bottom: 3px;" colspan="2" |<small>[[wikipedia:Chemical infobox|Disclaimer and references]]</small>
|-
|}
{{main|Water (molecule)}}

Water is the [[chemical substance]] with [[chemical formula]] '''[[hydrogen|H]]<sub>2</sub>[[oxygen|O]]''': one [[molecule]] of water has two [[hydrogen]] [[atom]]s [[covalent]]ly [[chemical bond|bonded]] to a single [[oxygen]] atom. Water is a tasteless, odourless liquid at [[standard conditions|ambient temperature and pressure]], and appears colourless in small quantities, although it has its own intrinsic very light blue hue. Ice also appears colourless, and water vapour is essentially invisible as a gas.<ref>[http://www.dartmouth.edu/~etrnsfer/water.htm Why is water blue?]</ref>
Water is primarily a liquid under standard conditions, which is not predicted from its relationship to other analogous hydrides of the [[Chalcogen|oxygen family]] in the [[periodic table]] which are gases, such as [[hydrogen sulfide]]. Also the elements surrounding oxygen in the [[periodic table]], [[nitrogen]], [[fluorine]], [[phosphorus]], [[sulfur]] and [[chlorine]], all combine with [[hydrogen]] to produce gases under standard conditions. The reason that oxygen hydride (water) forms a liquid is that it is more [[electronegative]] than all of these elements (other than fluorine). Oxygen attracts electrons much more strongly than hydrogen, resulting in a net positive charge on the hydrogen atoms, and a net negative charge on the oxygen atom. The presence of a charge on each of these atoms gives each water molecule a net [[dipole moment]]. Electrical attraction between water molecules due to this dipole pulls individual molecules closer together, making it more difficult to separate the molecules and therefore raising the boiling point. This attraction is known as [[hydrogen bonding]]. Water can be described as a polar liquid that dissociates disproportionately into the [[hydronium]] ion (H<sub>3</sub>O<sup>+</sup><sub>(aq)</sub>) and an associated [[hydroxide]] ion (OH<sup>-</sup><sub>(aq)</sub>).
Water is in [[dynamic equilibrium]] between the [[liquid]], [[gas]] and [[solid]] [[states of matter|states]] at [[standard temperature and pressure]], and is the only pure substance found naturally on Earth to be so.

===Cohesion and adhesion===
Water has a partial negative charge (σ-) near the oxygen atom due to the unshared pairs of electrons, and partial positive charges (σ+) near the hydrogen atoms. In water, this happens because the oxygen atom is more [[electronegative]] than the hydrogen atoms — that is, it has a stronger "[[electrostatic force|pulling power]]" on the molecule's [[electron]]s, drawing them closer (along with their negative charge) and making the area around the oxygen atom more negative than the area around both of the hydrogen atoms.

====Adhesion====
[[Image:Water drops on spider web.jpg|thumb|right|[[Dew]] drops adhering to a [[spider web]]]]
Water sticks to itself ([[cohesion (chemistry)|cohesion]]) because it is [[polar molecule|polar]].
Water also has high [[adhesion]] properties because of its polar nature. On extremely clean/smooth [[glass]] the water may form a thin film because the molecular forces between glass and water molecules (adhesive forces) are stronger than the cohesive forces.
In biological cells and [[organelle]]s, water is in contact with membrane and protein surfaces that are [[hydrophilic]]; that is, surfaces that have a strong attraction to water. [[Irving Langmuir]] observed a strong repulsive force between hydrophilic surfaces. To dehydrate hydrophilic surfaces — to remove the strongly held layers of water of hydration — requires doing substantial work against these forces, called hydration forces. These forces are very large but decrease rapidly over a nanometer or less. Their importance in biology has been extensively studied by [[V. Adrian Parsegian]] of the [[National Institute of Health]].<ref> [http://www.biophysics.org/education/parsegian.pdf Physical Forces Organizing Biomolecules (PDF)]</ref> They are particularly important when cells are dehydrated by exposure to dry atmospheres or to extracellular freezing.

====Surface tension====
{{main|Surface tension}}
[[Image:Dscn3156-daisy-water 1200x900.jpg|thumb|right|This [[daisy]] is under the water level, which has risen gently and smoothly. Surface tension prevents the water from submerging the flower.]]

Water has a high [[surface tension]] caused by the strong cohesion between water molecules. This can be seen when small quantities of water are put onto a non-soluble surface such as [[polythene]]; the water stays together as drops. Just as significantly, air trapped in surface disturbances forms bubbles, which sometimes last long enough to transfer gas molecules to the water.
Another surface tension effect is [[capillary wave]]s which are the surface ripples that form from around the impact of drops on water surfaces, and some times occur with strong subsurface currents flow to the water surface. The apparent elasticity caused by surface tension drives the waves.

====Capillary action====
{{main|Capillary action}}
[[Capillary action]] refers to the process of water moving up a narrow tube against the force of [[gravity]]. It occurs because water adheres to the sides of the tube, and then surface tension tends to straighten the surface making the surface rise, and more water is pulled up through cohesion. The process is repeated as the water flows up the tube until there is enough water that gravity can counteract the adhesive force.

===Solvation===
[[Image:Havasu Falls 2 md.jpg|thumb|200px|left|High concentrations of dissolved [[Lime (mineral)|lime]] make the water of [[Havasu Falls]] appear turquoise.]]
Water is a very strong [[solvent]], referred to as ''the universal [[solvent]]'', dissolving many types of substances. Substances that will mix well and dissolve in water (e.g. [[salt]]s) are known as "[[hydrophilic]]" (water-loving) substances, while those that do not mix well with water (e.g. [[lipids|fats and oils]]), are known as "[[hydrophobic]]" (water-fearing) substances. The ability of a substance to dissolve in water is determined by whether or not the substance can match or better the strong [[intermolecular force#Dipole-dipole interactions|attractive forces]] that water molecules generate between other water molecules. If a substance has properties that do not allow it to overcome these strong intermolecular forces, the molecules are "[[precipitation (chemistry)|pushed out]]" from amongst the water and do not dissolve.

===Electrical conductivity===
Pure water has a ''low'' [[electrical conductivity]], but this increases significantly upon solvation of a small amount of ionic material water such as [[hydrogen chloride]]. Thus the risks of [[electric shock|electrocution]] are much greater in water with the usual impurities not found in pure water. Any electrical properties observable in water are from the [[ion]]s of mineral salts and [[carbon dioxide]] dissolved in it. [[self-ionization of water|Water does self-ionize]] where two water molecules become one [[hydroxide]] anion and one [[hydronium]] cation, but not enough to carry enough [[electric current]] to do any work or harm for most operations. In pure water, sensitive equipment can detect a very slight electrical [[electrical conductivity|conductivity]] of 0.055 [[Siemens (unit)|µS]]/[[Centimeter|cm]] at 25°C. Water can also be [[electrolysis|electrolyzed]] into oxygen and hydrogen gases but in the absence of dissolved ions this is a very slow process since very little current is conducted.

=== Deuterated compounds of water ===

Hydrogen has 3 isotopes, the first being the most common, or having 1 proton and 0 neutrons. More than 95% of water consists of this regular water. There is a second isotope having 1 proton and 1 neutron, called [[deuterium]] (short form "D"). This {{chem|D|2|O}} is also known as [[heavy water]] and is used in [[nuclear reactor]]s for storing nuclear wastes. The third isotope has 1 proton and 2 neutrons, called [[tritium]]. Tritium is [[radioactive]], and therefore {{chem|T|2|O}} does not exist in nature as creation of the rare molecule would result in almost instantaneous decomposition. {{chem|D|2|O}} is stable; however, it is different from {{chem|H|2|O}} in that {{chem|D|2|O}} is heavier and denser, and it can block alpha and beta rays. {{chem|D|2|O}} occurs naturally in water in very low concentrations. Consumption of pure isolated {{chem|D|2|O}} may affect biochemical processes: ingestion of large amounts impairs [[kidney]] function and [[central nervous system]] operation.

===Water, ice, and vapor===
====Heat capacity and heat of vaporization====
{{main|Enthalpy of vaporization}}
Water has the second highest [[specific heat capacity]] of any known chemical compound, after [[ammonia]], as well as a high [[heat of vaporization]] (40.65 kJ mol<sup>-1</sup>), both of which are a result of the extensive [[hydrogen bond]]ing between its molecules. These two unusual properties allow water to moderate Earth's [[climate]] by buffering large fluctuations in temperature.

====Freezing point====
A simple but environmentally important and unusual property of water is that its usual solid form, [[ice]], floats on its liquid form. This solid state is not as dense as liquid water because of the geometry of the hydrogen bonds which are formed only at lower temperatures. For almost all other substances the solid form has a greater [[density]] than the liquid form. Fresh water at standard atmospheric pressure is most dense at 3.98 °C, and will sink by [[convection]] as it cools to that temperature, and if it becomes colder it will rise instead. This reversal will cause deep water to remain warmer than shallower freezing water, so that ice in a body of water will form first at the surface and progress downward, while the majority of the water underneath will hold a constant 4 °C. This effectively insulates a lake floor from the cold.
The water will freeze at 0°C (32°F, 273 K), however, it can be [[supercooled]] in a fluid state down to its [[nucleation|crystal homogeneous nucleation]] at almost 231 K (−42 °C).{{Fact|date=June 2007}}
Ice also has a number of more exotic phases not commonly seen (go to the full article on [[Ice]]).

====Triple point====
{{main|Triple point}}
The [[triple point]] of water (the single combination of pressure and temperature at which pure liquid water, ice, and water vapor can coexist in a stable equilibrium) is used to define the [[kelvin]], the SI unit of thermodynamic temperature. As a consequence, water's triple point temperature is an exact value rather than a measured quantity : 273.16 kelvins (0.01 °C) and a pressure of 611.73 pascals (approximately 0.0060373 [[atmosphere (unit)|atm]]).
This is approximately the combination that exists with 100% relative humidity at sea level and the freezing point of water.

====Miscibility and condensation====
{{main|Humidity}}
Water is [[miscible]] with many liquids, for example [[ethanol]] in all proportions, forming a single homogeneous liquid. On the other hand water and most [[oil]]s are ''immiscible'' usually forming layers according to increasing density from the top.

[[Image:Relative Humidity.png|thumb|200px|right|Red line shows saturation]]
As a gas, water vapor is completely [[miscible]] with air. On the other hand the maximum water vapor pressure that is thermodynamically stable with the liquid (or solid) at a given temperature is relatively low compared with total atmospheric pressure.
For example, if the vapor ''[[partial pressure]]''<ref>
The pressure due to water vapor in the air is called the '''partial pressure'''([[Dalton's law]]) and it is directly proportional to concentration of water molecules in air ([[Boyle's law]]).
</ref> is 2% of atmospheric pressure and the air is cooled from 25 deg C, starting at about 22 C water will start to condense, defining the [[dew point]], and creating [[fog]] or [[dew]]. The reverse process accounts for the fog ''burning off'' in the morning.
If one raises the humidity at room temperature, say by running a hot shower or a bath, and the temperature stays about the same, the vapor soon reaches the pressure for phase change, and condenses out as steam.
A gas in this context is referred to as ''saturated'' or 100% relative humidity, when the vapor pressure of water in the air is at the equilibrium with vapor pressure due to (liquid) water; water (or ice, if cool enough) will fail to lose mass through evaporation when exposed to saturated air. Because the amount of water vapor in air is small, ''relative humidity'', the ratio of the partial pressure due to the water vapor to the saturated partial vapor pressure, is much more useful.
Water vapor pressure above 100% relative humidity is called ''super-saturated'' and can occur if air is rapidly cooled, say by rising suddenly in an updraft.
<ref>
''[[Adiabatic process#Adiabatic heating and cooling|Adiabatic cooling]]'' resulting from the [[ideal gas law]].
</ref>

==Water on Earth==
===Origin and planetary effects===
[[Image:Habitable zone-en.svg|thumb|300px|right|The [[Solar System]] along center row range of possible [[habitable zone]]s of varying size stars.]]
Much of the universe's water may be produced as a byproduct of [[star formation]].
When stars are born, their birth 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 we observe is quickly produced in this warm dense gas.
<ref>
Gary Melnick, [[Harvard-Smithsonian Center for Astrophysics]] and David Neufeld, [[Johns Hopkins University]] quoted in:
{{cite news | title=Discover of Water Vapor Near Orion Nebula Suggests Possible Origin of H20 in Solar System [sic]| publisher=The Harvard University Gazette | date=April 23, 1998 | url=http://www.news.harvard.edu/gazette/1998/04.23/DiscoverofWater.html}}
{{cite news | title=Space Cloud Holds Enough Water to Fill Earth's Oceans 1 Million Times | publisher=Headlines@Hopkins, JHU | date= April 9, 1998| url=http://www.jhu.edu/news_info/news/home98/apr98/clouds.html }}
{{cite news | title=Water, Water Everywhere: Radio telescope finds water is common in universe | publisher=The Harvard University Gazette | date=February 25, 1999 | url=http://www.hno.harvard.edu/gazette/1999/02.25/telescope.html }}.
(linked 4/2007)
</ref>
====Solar distance and Earth gravity====
The existence of liquid water, and to a lesser extent its gaseous and solid forms, on Earth is vital to the existence of [[life on Earth]]. The Earth is located in the [[habitable zone]] of the [[solar system]]; if it were slightly closer to or further from the [[Sun]] (about 5%, or 8 million kilometers or so), the conditions which allow the three forms to be present simultaneously would be far less likely to exist.
<ref>J. C. I. Dooge. "Integrated Management of Water Resources". in E. Ehlers, T. Krafft. (eds.) ''Understanding the Earth System: compartments, processes, and interactions. Springer, '''2001''', p. 116. More references are at the end of the article "Habitable Zone" at [http://www.daviddarling.info/encyclopedia/H/habzone.html The Encyclopedia of Astrobiology, Astronomy and Spaceflight].
</ref>

Earth's mass allows [[gravity]] to hold an [[Celestial body atmosphere|atmosphere]]. Water vapor and carbon dioxide in the atmosphere provide a [[greenhouse effect]] which helps maintain a relatively steady surface temperature. If Earth were smaller, a thinner atmosphere would cause temperature extremes preventing the accumulation of water except in [[polar ice cap]]s (as on [[Mars (planet)|Mars]]).

It has been proposed that life itself may maintain the conditions that have allowed its continued existence. 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 also depends on a 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. [http://www.cnn.com/2007/TECH/space/05/16/odd.exoplanet.reut/index.html]

====Tides====
{{imageframe
|width=240
|content=[[Image:Bay of Fundy High Tide.jpg|120px]][[Image:Bay of Fundy Low Tide.jpg|120px]]
|caption=High tide (left) and low tide (right).
}}
{{main|Tide}}
'''[[Tide]]s''' are the cyclic rising and falling of [[Earth]]'s [[ocean]] surface caused by the [[tidal force]]s of the [[Moon]] and the [[Sun]] acting on the oceans. Tides cause changes in the depth of the marine and [[estuary|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 [[Coriolis effect|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.

=== Water cycle ===
<!--[[Image:Above the Clouds.jpg|right|thumb|150px|[[Cumulus mediocris]] clouds]]-->
The [[biosphere]] can be roughly divided into oceans, land, and atmosphere.
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 (meteorology)|precipitation]], from water vapor condensing from the air and falling to earth or ocean.
*[[runoff (water)|runoff]] from the land usually reaching the [[sea]].
<!--[[Image:WhereRainbowRises.jpg|right|100px|thumb|Rain [[refract]]s [[sunlight]] to produce this [[rainbow]].]]-->
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 36 [[Tonne#Multiples|Tt]] per year. Over land, evaporation and transpiration contribute another 71 Tt per year.
Precipitation, at a rate of 107 Tt per year over land, has several forms: most commonly [[rain]], [[snow]], and [[hail]], with some contribution from [[fog]] and [[dew]].
Condensed water in the air may also [[refract]] [[sunlight]] to produce [[rainbow]]s.

Water runoff often collects over [[Drainage basin|watershed]]s flowing into rivers.
Some of this is diverted to [[irrigation]] for agriculture. Rivers and seas offer opportunity for [[travel]] and [[commerce]]. Through [[erosion]], runoff shapes the environment creating river [[valley]]s and [[river delta|deltas]] which provide rich soil and level ground for the establishment of population centers.

===Fresh water storage===
Some runoff water is trapped for periods, 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.
Water also infiltrates the ground and goes into aquifers. This [[groundwater]] later flows back to the surface in [[spring (hydrosphere)|springs]], or more spectacularly in [[hot spring]]s and [[geyser]]s. Groundwater is also extracted artificially in [[water well|well]]s.
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.
[[Image:SnowflakesWilsonBentley.jpg|left|thumb|125px|''Snowflakes'' by [[Wilson Bentley]], 1902]]
===Forms of water===
{{seedetails|:Category: Forms of water}}
Water takes many different forms on Earth: [[water vapor]] and clouds in the sky; [[seawater]] and rarely [[iceberg]]s in the ocean; [[glacier]]s and rivers in the [[mountain]]s; and aquifers in the ground.
<!--
Because of the importance of precipitation to [[agriculture]], and to [[mankind]] in general, different names are given to its various forms:-->

Water can dissolve many different substances imparting upon it different tastes and odours. In fact, humans and other animals have developed senses to be able to evaluate the [[drinking water|potability]] of water: animals generally dislike the taste of [[salt]]y [[sea water]] and the putrid [[swamp]]s and favor the purer water of a mountain spring or aquifer. The taste advertised in [[spring water]] or [[mineral water]] derives from the minerals dissolved, while pure H<sub>2</sub>O is tasteless. As such, [[purity]] in spring and mineral water refers to purity from [[toxin]]s, [[pollutant]]s, and [[microorganism|microbe]]s.

== Effects on life ==
[[Image:Blue Linckia Starfish.JPG|thumb|right|Some of the [[biodiversity]] of a [[coral reef]]]]
From a [[biology|biological]] standpoint, water has many distinct properties that are critical for the proliferation of [[life]] that set it apart from other substances. It carries out this role by allowing [[organic compound]]s 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 [[metabolism|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). Water is thus essential and central to these metabolic processes. Therefore, without water, these metabolic processes would cease to exist, leaving us to muse about what processes would be in its place, such as gas absorption, dust collection, etc.

Water is also central to photosynthesis and respiration. Photosynthetic cells use the sun's energy to split off water's hydrogen from oxygen. Hydrogen is combined with CO<sub>2</sub> (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 CO<sub>2</sub> in the process (cellular respiration).

Water is also central to acid-base neutrality and enzyme function. An acid, a hydrogen ion (H<sup>+</sup>, that is, a proton) donor, can be neutralized by a base, a proton acceptor such as hydroxide ion (OH<sup>−</sup>) 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. Stomach acid (HCl) is useful to digestion. However, its corrosive effect on the esophagus during reflux can temporarily be neutralized by ingestion of a base such as [[aluminum hydroxide]] to produce the neutral molecules water and the salt aluminum chloride. Human biochemistry that involves enzymes usually performs optimally around a biologically neutral pH of 7.4.

===Aquatic life forms===
[[Image:Diatoms through the microscope.jpg|thumb|left|Some marine [[diatom]]s - a key [[phytoplankton]] group]]
Earth's waters are filled with life. Nearly all [[fish]] live exclusively in water, and there are many types of marine mammals, such as [[dolphin]]s and [[whale]]s that also live in the water. Some kinds of animals, such as [[amphibian]]s, 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.

Different water creatures have found different solutions to obtaining oxygen in the water. Fish have [[gills]] instead of [[lungs]], though some species of fish, such as the [[lungfish]], have both. [[Marine mammal]]s, such as dolphins, whales, [[otter]]s, and [[pinniped|seals]] need to surface periodically to breathe air.

==Effects on human civilization==
[[Image:Water.jpg|thumb|right|A [[shower]]]]
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]]. Large [[metropolis]]es like [[Rotterdam]], [[London]], [[Montreal]], [[Paris]], [[New York City]], [[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===
Water fit for [[human]] consumption is called [[drinking water]] or [[potable water]]. Water that is not potable can be made potable by distillation (heating it until it becomes water vapor, and then capturing the vapor without any of the impurities it leaves behind), or by other methods (chemical or heat treatment that kills bacteria). Sometimes the term [[safe water]] is applied to potable water of a lower quality threshold (i.e., it is used effectively for nutrition in humans that have weak access to water cleaning processes, and does more good than harm). 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).

This natural resource is becoming scarcer in certain places, and its availability is a major social and economic concern. Currently, about 1 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 [[29th G8 summit|2003 G8 Evian summit]].<ref> [http://www.g8.fr/evian/english/navigation/2003_g8_summit/summit_documents/water_-_a_g8_action_plan.html G8 "Action plan" decided upon at the 2003 Evian summit] </ref> 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 supplies and over 1 billion without access to adequate sanitation facilities. Poor water quality and bad sanitation are deadly; some 5 million deaths a year are caused by polluted drinking water. Water, however, is not a finite resource (like petroleum is), but rather re-circulated as potable water in precipitation in quantities many degrees 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, 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), since the manufacturing process uses around 10 to 100 times products' masses in water.

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 {{Fact|date=February 2007}}. The strain affects surface freshwater bodies like rivers and lakes, but it also degrades groundwater resources.

===Human uses===

====For Weighing====
One [[liter]] of water was used to determine the [[weight]] of a [[kilogram]]. Unfortunately, the measurement of water was taken at one degree [[Celsius]]{{Fact|date=July 2007}}. Water is its most dense at four degrees [[Celsius]]. Thus the measurement was actually not correct. {{Fact|date=July 2007}}

====For drinking====
[[Image:TapWater-china.JPG|thumb|right|A manual water [[pump]] in China]]
{{main|Drinking water}}
About 70% of the fat free mass of the [[human]] body is made of water.{{Fact|date=July 2007}} To function properly, the body requires between one and seven [[liter]]s 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 experts agree that 8–10 glasses of water (approximately 2 liters) daily is the minimum to maintain proper hydration.<ref>{{cite web |url=http://www.bbc.co.uk/health/healthy_living/nutrition/drinks_water.shtml |title=Healthy Water Living|producer=BBC|accessdate=2007-02-01}}</ref> For those who do not have kidney problems, 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]], which can be fatal. The "fact" that a person should consume eight glasses of water per day cannot be traced back to a scientific source.<ref>[http://ajpregu.physiology.org/cgi/content/full/283/5/R993 "Drink at least eight glasses of water a day." Really? Is there scientific evidence for "8 × 8"?] by Heinz Valdin, Department of Physiology, Dartmouth Medical School, Lebanon, [[New Hampshire]]</ref> There are other myths such as the effect of water on weight loss and constipation that have been dispelled.<ref> [http://www.factsmart.org/h2o/h2o.htm Drinking Water - How Much?], Factsmart.org web site and references within</ref>

Original recommendation for water intake in 1945 by the [[Food and Nutrition Board]] of the [[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."<ref>Food and Nutrition Board, National Academy of Sciences. Recommended Dietary Allowances, revised 1945. National Research Council, Reprint and Circular Series, No. 122, 1945 (Aug), p. 3-18.</ref> The latest dietary reference intake report by the [[United States National Research Council]] in general recommended (including food sources): 2.7 liters of water total for women and 3.7 liters for men.<ref>[http://www.iom.edu/report.asp?id=18495 Dietary Reference Intakes: Water, Potassium, Sodium, Chloride, and Sulfate], Food and Nutrition Board</ref> Specifically, [[Pregnancy|pregnant]] and [[breastfeeding]] women need additional fluids to stay hydrated. According to the [[Institute of Medicine]] &mdash; who recommend that, on average, women consume 2.2 litres and men 3.0 litres &mdash; this is recommended to be 2.4 litres (approx. 9 cups) for pregnant women and 3 litres (approx. 12.5 cups) for breastfeeding women since an especially large amount of fluid is lost during nursing.<ref>http://www.mayoclinic.com/health/water/NU00283</ref> Also noted is that normally, about 20 percent of water intake comes from food, while the rest comes from drinking water and beverages ([[Caffeine|caffeinated]] included). Water is excreted from the body in multiple forms; through [[urine]] and [[feces]], through [[sweat]]ing, 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 that does not contain too many impurities. Common impurities include metal salts and/or harmful [[bacterium|bacteria]], such as ''[[Vibrio]]''. Some [[solutes]] are acceptable and even desirable for taste enhancement and to provide needed [[electrolyte]]s.

The single largest freshwater resource suitable for drinking is the [[Lake Baikal]] in Siberia, which has a very low [[salt]] and [[calcium]] content and is very clean.

====As a solvent====
[[Dissolving]] (or [[suspension (chemistry)|suspending]]) is used to wash everyday items such as the human body, clothes, floors, cars, food, and pets.

====As a thermal transfer agent====
[[Boiling]], [[steaming]], and [[simmering]] are popular [[cooking]] methods that often require immersing food in water or its gaseous state, steam. Water is also used in industrial contexts as a [[coolant]], and in almost all power-stations as a coolant and to drive steam [[turbine]]s to generate electricity. In the nuclear industry, water can also be used as a [[neutron moderator]].

====Recreation====

Humans use water for many recreational purposes, as well as for exercising and for sports. Some of these include [[swimming]], [[waterskiing]], [[boating]], [[fishing]], and [[diving]]. In addition, some sports, like [[ice hockey]] and [[ice skating]], are played on ice.
[[Image:BoatsonMiamiBeach.jpg|thumb|right|Some boats in a [[harbor]] in [[Miami Beach, Florida]]]]
Lakesides and beaches are popular places for people to go to relax and enjoy recreation. Many find the sound of flowing water to be calming, too. Some keep fish and other life in [[aquarium|water tanks]] or [[pond]]s for show, fun, and companionship. Humans also use water for snow sports i.e. [[skiing]] or [[snowboarding]], which requires the water to be frozen.
People may also use water for [[play fighting]] such as with [[snowball]]s, [[water gun]]s or [[water balloon]]s.

====Industrial applications====
Pressurized water is used in [[water blasting]] and [[water jet cutter]]s. 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.
{{sect-stub}}

====Food processing====
Water 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 is affected by solutes. One [[mole (unit)|mole]] of sucrose (sugar) raises the boiling point of water by 0.52 °C, and one mole of salt raises the boiling point by 1.04 °C while lowering the freezing point of water in a similar way.<ref name="vaclacik">Vaclacik and Christian, 2003</ref> Solutes in water also affect water activity which affects many chemical reactions and the growth of microbes in food.<ref name="deman">DeMan, 1999</ref> Water activity can be described as a ratio of the vapor pressure of water in a solution to the vapor pressure of pure water.<ref name="vaclacik"/> Solutes in water lower water activity. This is important to know because most bacterial growth ceases at low levels of water activity.<ref name="deman" /> 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. It can dramatically affect the quality of a product as well as playing a role in sanitation. Water hardness is classified based on the amounts of removable calcium carbonate salt it contains per gallon. Water hardness is measured in grains; 0.064 g calcium carbonate is equivalent to one grain of hardness.<ref name="vaclacik"/> Water is classified as soft if it contains 1 to 4 grains, medium if it contains 5 to 10 grains and hard if it contains 11 to 20 grains.<ref name="vaclacik"/> The hardness of water may be altered or treated by using a chemical ion exchange system. The hardness of water also affects its pH balance which plays a critical role in food processing. For example, hard water prevents successful production of clear beverages. Water hardness also affects sanitation; with increasing hardness, there is a loss of effectiveness for its use as a sanitizer.<ref name="vaclacik"/>

====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.

==Politics==
{{seealso|Water resources|Category:Water and politics}}
[[Image:Evstafiev-bosnia-sarajevo-water-line.jpg|thumb|left|People waiting in line to gather water during the [[Siege of Sarajevo]]]]

Because of [[overpopulation]], [[mass consumption]], misuse, and [[water pollution]], the availability of drinking water [[per capita]] is inadequate and shrinking as of the year 2006. For this reason, water is a strategic resource in the globe and an important element in many political conflicts. Some have predicted that clean water will become the "next oil"{{Fact|date=February 2007}}, making [[Canada]], with this resource in abundance, possibly the richest country in the world. There is a long history of conflict over water, including efforts to gain access to water, the use of water in wars started for other reasons, and tensions over shortages and control.<ref> [http://www.worldwater.org/conflict.html A Chronology of Water-Related Conflicts] </ref> [[UNESCO]]'s World Water Development Report (WWDR, 2003) from its [[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 [[disease]]s 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]]. Fresh water &mdash; now more precious than ever in our history for its extensive use in agriculture, high-tech manufacturing, and energy production &mdash; is increasingly receiving attention as a resource requiring better management and sustainable use.

=== OECD countries ===
[[Image:Hopetoun falls.jpg|thumb|right|350px|Hopetoun Falls near [[Otway National Park]], [[Victoria, Australia]]]]
With nearly 2,000&nbsp;[[cubic metres]] (70,000&nbsp;ft<sup>3</sup>) of water per person and per year, the [[United States]] leads the world in water consumption per capita. In the Organization for Economic Co-operation and Development ([[OECD]]) countries, the U.S. is first for water consumption, then [[Canada]] with 1,600&nbsp;cubic&nbsp;meters (56,000&nbsp;ft<sup>3</sup>) of water per person per year, which is about twice the amount of water used by the average person from [[France]], three times as much as the average [[Germany|German]], and almost eight times as much as the average [[Denmark|Dane]]. Since 1980, overall water use in Canada has increased by 25.7%. This is five times higher than the overall OECD increase of 4.5%. In contrast, nine OECD nations were able to decrease their overall water use since 1980 ([[Sweden]], the [[Netherlands]], the United States, the [[United Kingdom]], the [[Czech Republic]], [[Luxembourg]], [[Poland]], [[Finland]] and Denmark).<ref> [http://www.environmentalindicators.com/htdocs/indicators/6wate.htm Water consumption indicator] in the [[OECD]] countries </ref><ref> {{cite news | title=Golf 'is water hazard' | publisher=BBC News | date=March 17, 2003 | url=http://news.bbc.co.uk/1/hi/sci/tech/2857587.stm}} </ref>

===United States===
Ninety-five percent of the United States' fresh water is underground. One crucial source is a huge underground reservoir, the 1,300-kilometer (800&nbsp;mi) [[Ogallala Aquifer|Ogallala aquifer]] which stretches from [[Texas]] to [[South Dakota]] and waters one fifth of U.S. irrigated land. Formed over millions of years, the Ogallala aquifer has since been cut off from its original natural sources. It is being depleted at a rate of 12 billion cubic meters (420&nbsp;billion&nbsp;ft<sup>3</sup>) per year, amounting to a total depletion to date of a volume equal to the annual flow of 18 [[Colorado River]]s. Some estimates say it will dry up in as little as 25 years. Many farmers in the [[High Plains (United States)|Texas High Plains]], which rely particularly on the underground source, are now turning away from [[irrigated agriculture]] as they become aware of the hazards of overpumping.<ref> {{cite news | title=Ogallala aquifer - Water hot spots | publisher=BBC News | date=? | url=http://news.bbc.co.uk/1/shared/spl/hi/world/03/world_forum/water/html/ogallala_aquifer.stm}} </ref>

=== Mexico ===
{{See also|Water supply and sanitation in Mexico}}

In [[Mexico City]], an estimated 40% of the city's water is lost through leaky pipes built at the turn of the 20th century.<ref>{{cite news | title=Mexico City - Water hot spots | publisher=BBC News | date=? | url=http://news.bbc.co.uk/1/shared/spl/hi/world/03/world_forum/water/html/mexico_city.stm}} </ref>

=== Middle East ===
The [[Middle East]] region has only 1% of the world's available fresh water, which is shared among 5% of the world's population. Thus, in this region, water is an important strategic resource. By 2025, it is predicted that the countries of the Arabian peninsula will be using more than double the amount of water naturally available to them.<ref> {{cite news | title=Water shortages 'foster terrorism' | publisher=BBC News | date=March 18, 2003 | url=http://news.bbc.co.uk/1/hi/sci/tech/2859937.stm}} </ref> According to a report by the [[Arab League]], two-thirds of Arab countries have less than 1,000&nbsp;cubic meters (35,000&nbsp;ft<sup>3</sup>) of water per person per year available, which is considered the limit.<ref> "Major aspects of scarce water resources management with reference to the Arab countries", Arab League report published for the International Conference on water gestion and water politics in arid zones, in Amman, Jordan, December 1-3, 1999. Quoted by French journalist [[Christian Chesnot]] in {{cite news | title=Drought in the Middle East | publisher=Monde diplomatique | date=February 2000 | url=http://mondediplo.com/2000/02/08chesnot}} - French original version freely available [http://www.monde-diplomatique.fr/2000/02/CHESNOT/13213.html here].</ref>

{{TotallyDisputed}}

[[Jordan]], for example, has little water, and [[dam]]s in other countries have reduced its available water sources over the years. The 1994 [[Israel-Jordan Treaty of Peace]] stated that Israel would give 50 million cubic meters of water (1.7&nbsp;billion&nbsp;ft<sup>3</sup>) per year to Jordan, which it refused to do in 1999 before backtracking. The 1994 treaty stated that the two countries would cooperate in order to allow Jordan better access to water resources, notably through dams on the [[Yarmouk River]].<ref> See 1994 [[Israel-Jordan Treaty of Peace]], annex II, article II, first paragraph </ref> Confronted by this lack of water, Jordan is preparing new techniques to use non-conventional water resources, such as second-hand use of irrigation water and [[desalinization]] techniques, which are very costly and are not yet used. A desalinization project will soon be started in [[Hisban]], south of [[Amman]]. The [[Disi]] [[groundwater]] project, in the south of Jordan, will cost at least $250 million to bring out water. Along with the [[Unity Dam]] on the Yarmouk River, it is one of Jordan's largest strategic projects. Born in 1987, the "Unity Dam" would involve both Jordan and [[Syria]]. This "Unity Dam" still has not been implemented because of [[Israel]]'s opposition, Jordan and Syrian conflictive relations and refusal of world investors. However, Jordan's reconciliation with Syria following the death of [[Hussein of Jordan|King Hussein]] represents the removal of one of the project's greatest obstacles.<ref name="drought_middle_east"> See [[Christian Chesnot]] in {{cite news | title=Drought in the Middle East | publisher=[[Le Monde diplomatique]] | date=February 2000 | url=http://mondediplo.com/2000/02/08chesnot}} - French original version freely available [http://www.monde-diplomatique.fr/2000/02/CHESNOT/13213.html here]. </ref>

[[Image:Hayarden.jpg|thumb|left|200px|The [[Jordan River]]]]
Both [[Israel]] and Jordan rely on the [[Jordan River]], but Israel controls it, as well as 90% of the water resources in the region. Water is also an important issue in the [[Israeli-Palestinian conflict|conflict with the Palestinians]] - indeed, according to former Israeli prime minister [[Ariel Sharon]] quoted by Abel Darwish in the BBC, it was one of the causes of the [[Six-Day War|1967 Six-Day War]]. In practice the access to water has been a [[casus belli]] for Israel. The [[Tsahal|Israeli army]] prohibits [[Palestine|Palestinians]] from pumping water, and [[Israeli settlements|settlers]] use much more advanced pumping equipment. Palestinians complain of a lack of access to water in the region.<ref> {{cite news | title=Analysis: Middle East water wars, by Abel Darwish | publisher=BBC News | date=May 30, 2003 | url=http://news.bbc.co.uk/2/hi/middle_east/2949768.stm}} </ref> Israelis in the [[West Bank]] use four times as much water as their Palestinian neighbors.<ref> {{cite news | title=Israel - water hot spots | publisher=BBC News | date=? | url=http://news.bbc.co.uk/1/shared/spl/hi/world/03/world_forum/water/html/israel.stm}} </ref> According to the [[World Bank]], 90% of the [[West Bank]]'s water is used by Israelis.<ref name="drought_middle_east" /> Article 40 of the appendix B of the [[September 28]], [[1995]] [[Oslo accords]] stated that "Israel recognizes Palestinians' rights on water in the West Bank".

The [[Golan]] Heights provide 770 million cubic meters (27&nbsp;billion&nbsp;ft<sup>3</sup>) of water per year to Israel, which represents a third of its annual consumption. The Golan's water goes to the [[Sea of Galilee]] &mdash; Israel's largest reserve &mdash; which is then redistributed throughout the country by the [[National Water Carrier]]. The Golan, which Israel annexed, represents a strategic territory for Israel because of its water resources.<ref name="drought_middle_east" />. However, the level on the Sea of Galilee has dropped over the years, sparking fears that Israel's main water reservoir will become salinated. On its northern border, Israel threatened military action in 2002 when [[Lebanon]] opened a new pumping station taking water from a river feeding the Jordan. To help ease the crisis, Israel has agreed to buy water from [[Turkey]] and is investigating the construction of desalination plants.<ref> {{cite news | title=Israel - water hot spots | publisher=BBC News | date=? | url=http://news.bbc.co.uk/1/shared/spl/hi/world/03/world_forum/water/html/israel.stm}} </ref>

[[Iraq]] and [[Syria]] watched with apprehension the construction of the [[Atatürk Dam]] in Turkey and a projected system of 22 dams on the [[Tigris]] and [[Euphrates]] rivers.<ref> {{cite news | title=Turkey - water hot spots | publisher=BBC News | date=? | url=http://news.bbc.co.uk/1/shared/spl/hi/world/03/world_forum/water/html/turkey.stm}} </ref> According to the BBC, the list of 'water-scarce' countries in the region grew steadily from three in 1955 to eight in 1990 with another seven expected to be added within 20 years, including three [[Nile]] nations (the Nile is shared by nine countries).

=== Asia ===
[[Image:200407-sandouping-sanxiadaba-4.med.jpg|thumb|300px|Three Gorges Dam, receiving, upstream side, [[26 July]], [[2004]]]]
In [[Asia]], [[Cambodia]] and [[Vietnam]] are concerned by [[China]]'s and [[Laos]]' attempts to control the flux of water. China is also preparing the [[Three Gorges Dam]] project on the [[Yangtze River]], which would become the world's largest [[dam]], causing many social and environmental problems. It also has a project to divert water from the Yangtze to the dwindling [[Yellow River]], which feeds China's most important farming region.

[[Image:Ganges River Delta, Bangladesh, India.jpg|thumb|left|Ganges [[river delta]], Bangladesh and India]]
The [[Ganges]] is disputed between [[India]] and [[Bangladesh]]. The water reserves are being quickly depleted and polluted, while the [[glacier]] feeding the sacred [[Hinduism|Hindu]] river is retreating hundreds of feet each year because of [[global warming]]{{Fact|date=February 2007}} and [[deforestation]] in the [[Himalayas]], which is causing subsoil streams flowing into the Ganges river to dry up. Downstream, India controls the flow to [[Bangladesh]] with the [[Farakka Barrage]], 10&nbsp;kilometers (6&nbsp;mi) on the Indian side of the border. Until the late 1990s, India used the barrage to divert the river to [[Calcutta]] to keep the city's port from drying up during the dry season. This denied Bangladeshi farmers water and [[silt]], and it left the [[Sundarban]] wetlands and [[mangrove]] forests at the river's delta seriously threatened. The two countries have now signed an agreement to share the water more equally. Water quality, however, remains a problem, with high levels of [[arsenic]] and untreated sewage in the river water.<ref> {{cite news | title=Ganges river - water hot spots | publisher=BBC News | date=? | url=http://news.bbc.co.uk/1/shared/spl/hi/world/03/world_forum/water/html/river_ganges.stm}} </ref>

=== South America ===
The [[Guaraní Aquifer]], located between the [[Mercosur]] countries of [[Argentina]], [[Brazil]], [[Bolivia]] and [[Paraguay]], with a volume of about 40,000&nbsp;km³, is an important source of fresh potable water for all four countries.

=== Privatization ===
[[Privatization]] of water companies has been contested on several occasions because of poor water quality, increasing prices, and ethical concerns. In [[Bolivia]] for example, the proposed privatization of water companies by the [[IMF]] was met by [[Cochabamba protests of 2000|popular protests in Cochabamba in 2000]], which ousted [[Bechtel]], an American engineering firm based in [[San Francisco]]. [[SUEZ]] has started retreating from South America because of similar protests in [[Buenos Aires]], [[Santa Fe, Argentina|Santa Fe]], and [[Córdoba, Argentina]]. Consumers took to the streets to protest water rate hikes of as much as 500% mandated by SUEZ. In South and Central America, SUEZ has water concessions in Argentina, Bolivia, Brazil and Mexico. "Bolivian officials fault SUEZ for not connecting enough households to water lines as mandated by its contract and for charging as much as $455 a connection, or about three times the average monthly salary of an office clerk", according to the ''[[Mercury News]]''.<ref> {{cite news | title=Bolivia's water wars coming to end under Morales | publisher=[[Mercury News]] | date=February 26, 2006 | url=http://www.mercurynews.com/mld/mercurynews/news/world/13969197.htm}} </ref>

[[South Africa]] also made moves to privatize water, provoking an outbreak of cholera killing 200.<ref> {{cite news | title=Water privatisation: ask the experts | publisher=BBC News | date=December 10, 2004 | url=http://news.bbc.co.uk/2/hi/talking_point/2957550.stm}} </ref>

In 1997, World Bank consultants assisted the Philippine government in the privatization of the city of Manila's Metropolitan Waterworks and Sewerage Systems (MWSS). By 2003, water price increases registered at 81% in the east zone of the Philippines and 36% in the west region. As services became more expensive and inefficient under privatization, there was reduced access to water for poor households. In October 2003, the Freedom from Debt Coalition reported that the diminished access to clean water resulted in an outbreak of cholera and other gastro-intestinal diseases.<ref> {{cite news | title=Rights Education Empowers People in the Philippines | publisher=[[Aurora Parong]] | date=1995 | url=http://www.columbia.edu/cu/humanrights/publications/rn/rn_2004_5.htm}} </ref>

=== Regulation ===
[[Image:Water carrier.jpg|right|thumb|220px|A water-carrier in India, circa ~1882. In many places where running water is not available, water has to be transported by people.]]
Drinking water is often collected at [[spring (hydrosphere)|springs]], extracted from artificial [[Boring (mechanical)|borings]] in the ground, or wells. 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 are rainwater and river or lake water. This surface water, however, must be [[water purification|purified]] for human consumption. This may involve removal of undissolved substances, dissolved substances and harmful [[microbe]]s. Popular methods are [[filter (water)|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 [[ocean]] or [[seawater]] is a more expensive solution used in coastal [[arid]] [[climate]]s.

The distribution of drinking water is done through [[municipal water system]]s or as [[bottled water]]. Governments in many countries have programs to distribute water to the needy at no charge. Others argue that the [[market]] mechanism and [[free enterprise]] are best to manage this rare resource and to finance the boring of wells or the construction of dams and [[reservoir (water)|reservoirs]].

Reducing waste by using drinking 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 [[externality|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 victim of this pollution. [[Pharmaceuticals]] consumed by humans often end up in the waterways and can have detrimental effects on [[marine biology|aquatic]] life if they [[bioaccumulation|bioaccumulate]] and if they are not [[biodegradable]].

==Religion, philosophy, and literature==
[[Image:Hindu water ritual.jpg|thumb|225px|A Hindu ablution as practiced in [[Tamil Nadu]]]] <!-- I'd welcome a more precise description of this rite. -->

Water is considered a purifier in most religions. Major faiths that incorporate ritual washing ([[ablution]]) include [[Hinduism]], [[Christianity]], [[Islam]], [[Judaism]], and [[Shinto]]. Water [[baptism]] is a central [[sacrament]] of Christianity; 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 including Judaism and Islam. In Islam, the five daily prayers can be done in [[Tayammum|most cases]] after completing washing certain parts of the body using clean water (''[[wudu]]''). In Shinto, water is used in almost all rituals to cleanse a person or an area (e.g., in the ritual of ''[[misogi]]''). Water is mentioned in the [[Bible]] 442 times in the [[New International Version]] and 363 times in the [[King James Version]]: 2 Peter 3:5(b) states, "The earth was formed out of water and by water" (NIV).

Some faiths use water especially prepared for religious purposes ([[holy water]] in some Christian denominations, ''[[Amrit]]'' in Sikhism and Hinduism). Many religions also consider particular sources or bodies of water to be sacred or at least auspicious; examples include [[Lourdes]] in [[Roman Catholicism]], the [[Zamzam Well]] in Islam and the River [[Ganges]] (among many others) in Hinduism. In Neo-Paganism water is often combined with salt in the first steps of a ritual, to act as a purifier of worshippers and the altar, symbolising both cleansing tears and the ocean.

Water is often believed to have spiritual powers. In [[Celtic mythology]], [[Sulis]] is the local [[goddess]] of thermal springs; in [[Hinduism]], the [[Ganga in Hinduism|Ganges]] is also personified as a goddess, while [[Saraswati]] have been referred to as goddess in [[Veda]]s. Also water is one of the "panch-tatva"s (basic 5 elements, others including [[fire]], [[earth]], [[space]], [[air]]). Alternatively, gods can be patrons of particular springs, rivers, or lakes: for example in [[Greek mythology|Greek]] and [[Roman mythology|Roman]] [[mythology]], [[Peneus]] was a river god, one of the three thousand [[Oceanid]]s. In [[Islam]], not only does water give life, but every life is itself made of water: "We made from water every living thing".<ref> [[Sura]] of [[Al-Anbiya]] 21:30</ref>

The [[Ancient Greece|Greek]] [[philosopher]] [[Empedocles]] held that water is one of the four [[classical element]]s along with [[fire]], [[earth]] and [[Air (classical element)|air]], and was regarded as the [[ylem]], or basic substance of the universe. Water was considered cold and moist. In the theory of the four [[four humours|bodily humor]]s, water was associated with [[phlegm]]. [[Water (classical element)|Water]] was also one of the [[Five elements (Chinese philosophy)|five elements]] in traditional [[Chinese philosophy]], along with [[earth (classical element)|earth]], [[fire (classical element)|fire]], [[wood (classical element)|wood]], and [[metal (classical element)|metal]].

Water also plays an important role in [[literature]] as a [[symbol]] of [[purification]]. Examples include the critical importance of a [[river]] in ''[[As I Lay Dying]]'' by [[William Faulkner]] and the [[drowning]] of Ophelia in ''[[Hamlet]]''.

== See also ==
: ''Main lists: [[List of water related topics]] and [[List of water related topics by water type|List by water type]]''
{{col-begin}}
{{col-1-of-3}}
* [[Atmospheric water generator]]
* [[Bioswale]]
* [[Carbonation]]
* [[Cistern]]
* [[Color of water]]
* [[Dehydration]] (hypohydration) vs. [[hyperhydration]]
* [[Desalination]]
* [[Dihydrogen monoxide hoax]]
* [[Distilled water]]
* [[Drinking water]]
* [[Drought]]
* [[Ecohydrology]]
* [[Evapotranspiration]]
* [[Flood]]
* [[Fresh water]]
* [[Heavy water]]
* [[Hydrological transport model]]
* [[Hydrography]]
* [[Hydrology]]
* [[Hydropower]]
{{col-2-of-3}}
* [[Hydrosphere]]
* [[Ice]]
* [[Irrigation]]
* [[Mineral water]]
* [[Origin of water on Earth]]
* [[Precipitation (meteorology)]]
* [[Rain]]
* [[Rainwater harvesting]]
* [[Safe water]]
* [[Sea water]]
* [[Spring water]]
* [[Steam]]
* [[Tide]]
* [[United Nations Convention to Combat Desertification]] (UNCCD).
* [[Virtual water]]
* [[Wastewater]]
* [[Water 1st]] (non-profit organization)
* [[WaterAid]] (international non-profit organisation).
* [[Water crisis]]
{{col-3-of-3}}
* [[Water (molecule)]] - [[Water (data page)]]
* [[Water cycle]]
* [[Water fuel cell]]
* [[Water industry]]
* [[Water intoxication]]
* [[Water ionizer]]
* [[Water law]]
* [[Water memory]]
* [[Water park]]
* [[Water purification]]
* [[Water quality]]
* [[Water resources]]
* [[Water right]]
* [[Water sport (recreation)]]
* [[Water tank]]
* [[Water torture]]
* [[World Ocean Day]]
* [[World Water Day]]
{{col-end}}
{{portalpar|Water|Drinking water.jpg}}
{{Portalpar|Sustainable development|Sustainable development.svg}}

== References ==
===Cited references===
<div class="references-small">
<references/>
</div>
* {{cite book | title=Principles of Food Chemistry 3rd Edition | year=1999 | author=John M. DeMan}}
* {{cite book | title= Essentials of Food Science 2nd Edition | year=2003 | author= Vickie A. Vaclavik and Elizabeth W. Christian}}

===General references===
* OA Jones, JN Lester and N Voulvoulis, Pharmaceuticals: a threat to drinking water? ''TRENDS in Biotechnology'' 23(4): 163, 2005
* Franks, F (Ed), Water, A comprehensive treatise, Plenum Press, New York, 1972-1982
* [http://twt.mpei.ac.ru/mas/worksheets/VTP_wsp.mcd Property of Water and Water Steam w Thermodynamic Surface]
* PH Gleick and associates, The World's Water: The Biennial Report on Freshwater Resources. Island Press, Washington, D.C. (published every two years, beginning in 1998.)
* Marks, William E., The Holy Order of Water: Healing Earth's Waters and Ourselves. Bell Pond Books ( a div. of Steiner Books), Great Barrington, MA, November 2001 [ISBN 0-88010-483-X]
* Debenedetti, P. G., and Stanley, H. E.; "Supercooled and Glassy Water", ''Physics Today'' '''56''' (6), p. 40&ndash;46 (2003). [http://polymer.bu.edu/hes/articles/ds03.pdf Downloadable PDF (1.9 MB)]

=== Water as a natural resource ===
* {{cite book | title=The World's Water: The Biennial Report on Freshwater Resources | first=Peter H. | last=Gleick | location=Washington | publisher=Island Press}} (November 10, 2006)| ISBN-13: 9781597261050]
* {{cite book | title=Last Oasis: Facing Water Scarcity | year=1997, second edition| first=Sandra | last=Postel | location=New York | publisher=Norton Press}}
* {{cite book | title=Water Rights: Scarce Resource Allocation, Bureaucracy, and the Environment | year=1991| author=Anderson}}
* {{cite book | title=Water: The Fate of Our Most Precious Resource | year=2003, revised edition| author=Marq de Villiers}}
* {{cite book | title=Water Wars: Drought, Flood, Folly and the Politics of Thirst | year=2002 | author=Diane Raines Ward}}
* {{cite book | title=Water and Power: The Politics of a Scarce Resource in the Jordan River Basin | year=1995| author=Miriam R. Lowi}} (Cambridge Middle East Library)
* {{cite book | title=Rivers of Empire: Water, Aridity, and the Growth of the American West | year=1992 | first=Donald | last=Worster}}
* {{cite book | title=Cadillac Desert: The American West and Its Disappearing Water | year=1993 | first=Marc | last=Reisner}}
* {{cite book | title=Blue Gold: The Fight to Stop the Corporate Theft of the World's Water | author=Maude Barlow, Tony Clarke | year=2003}}
* {{cite book | title=Water Wars: Privatization, Pollution, and Profit | author=Vandana Shiva | year=2002 | id=ISBN 0-7453-1837-1}}
* {{cite book | title=Troubled Water: Saints, Sinners, Truth And Lies About The Global Water Crisis | author=Anita Roddick, et al | year=2004}}
* {{cite book | title=The Holy Order of Water: Healing Earths Waters and Ourselves | author=William E. Marks | year=2001}}

==External links==
{{commons|water}}
{{wiktionary}}
{{wikiquote}}
{{Wikinews}}

* [http://www.awra.org/ American Water Resources Association]
* [http://www.wateraid.org/ WaterAid - Charity dedicated to the provision of clean water, sanitation and hygiene education]


{{BranchesofFoodChemistry}}

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[[Category:Water| ]]
[[Category:Natural resources]]
[[Category:Oxygen compounds]]
[[Category:Hydrogen compounds]]

{{Link FA|ar}}
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[[als:Wasser]]
[[ar:ماء]]
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[[ast:Agua]]
[[az:Su]]
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[[be-x-old:Вада]]
[[bar:Wossa]]
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[[ru:Вода]]
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[[ru-sib:Волога]]
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[[zh:水]]

Revision as of 23:05, 22 July 2007


Water is your urine evaporated and cleaned. Also known as H2O

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