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| + | Water is the most abundant material on the earth. Its chemical name is H2O, ant it consists of two hyrdrogen atoms and one oxygen atom joined with two covalent bonds. It sometimes falls from the sky, in a process that is usually referred to as rain. |
| − | {{two other uses|the chemical substance|its chemical and physical properties|water (molecule)}}
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| − | [[Image:Iceberg with hole near sanderson hope 2007-07-28 2.jpg|right|350px|thumb|Water in three states: Liquid, solid ([[ice]]), and (invisible) vapor in air. [[Clouds]] are droplets of liquid, [[Condensation|condensed]] from [[water vapor]].]]
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| − | '''Water''' is a common [[chemical substance]] that is essential for the survival of all known forms of [[life]].<ref>[http://pubs.acs.org/cgi-bin/abstract.cgi/bichaw/1997/36/i43/abs/bi971323j.html The Lubricant of Life: A Proposal That Solvent Water Promotes Extremely Fast Conformational Fluctuations in Mobile Heteropolypeptide Structure<!-- Bot generated title -->]</ref>
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| − | 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|petatonnes]] (Pt) of water covers 71% of the [[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>
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| − | [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/dewa/assessments/ecosystems/water/vitalwater/ Vital Water] [[UNEP]].</ref> Some of the Earth's water is contained within man-made and natural objects near the Earth's surface such as [[water tower]]s, animal and plant bodies, manufactured products, and food stores.
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| − | [[Seawater|Saltwater]] [[ocean]]s hold 97% of surface water, [[glacier]]s and polar [[ice cap]]s 2.4%, and other land surface water such as [[river]]s, [[lake]]s and [[pond]]s 0.6%. Water moves continually through a [[water cycle|cycle]] of [[evaporation]] or [[transpiration]] ([[evapotranspiration]]), [[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 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 varying periods in ice caps, glaciers, aquifers, or in lakes, sometimes providing fresh water for life on land. Clean, fresh water is essential to [[human]] and other life. However, in many parts of the world - especially [[Third World|developing]] countries - it is in short supply. Water is a [[solvent]] for a wide variety of chemical substances.
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| − | == Types of water ==
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| − | [[Image:Water_slow_motion.ogg|thumb|125px|Liquid water in motion]]
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| − | Water can appear in three [[Phase (matter)|phases]]. 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 [[river]]s in the [[mountain]]s; and aquifers in the ground.
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| − | Water can dissolve many different substances, giving it different tastes and odors. 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. Humans also tend to prefer cold water rather than lukewarm, as cold water is likely to contain less [[microorganism|microbe]]s. The taste advertised in [[spring water]] or [[mineral water]] derives from the minerals dissolved in it, as 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.
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| − | Because of the importance of precipitation to [[agriculture]], and to [[mankind]] in general, different names are given to its various forms:
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| − | [[Image:SnowflakesWilsonBentley.jpg|right|thumb|125px|''[[Snowflake]]s'' by [[Wilson Bentley]], 1902]]
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| − | *'''according to phase'''
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| − | **solid - [[ice]]
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| − | **liquid - water, ([[Supercooling|supercooled]] water)
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| − | **gaseous - [[water vapor]]
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| − | *'''according to [[meteorology]]''':
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| − | **[[hydrometeor]]
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| − | ***[[Precipitation (meteorology)|precipitation]]
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| − | :{| border=0|
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| − | '''
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| − | |-
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| − | | ||precipitation according to moves|| ||precipitation according to phase
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| − | |-
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| − | |valign=top |
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| − | *vertical (falling) precipitation
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| − | **[[rain]]
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| − | **freezing rain
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| − | **[[drizzle]]
| + | |
| − | **freezing drizzle
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| − | **[[snow]]
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| − | **[[snow pellets]]
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| − | **[[snow grains]]
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| − | **[[ice pellets]]
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| − | **frozen rain
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| − | **[[hail]]
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| − | **[[ice crystals]]
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| − | *horizontal (seated) precipitation
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| − | ** [[dew]]
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| − | ** [[hoarfrost]]
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| − | ** [[atmospheric icing]]
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| − | ** [[glaze ice]]
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| − | ||
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| − | |valign=top |
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| − | *liquid precipitation
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| − | **[[rain]]
| + | |
| − | **freezing rain
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| − | **[[drizzle]]
| + | |
| − | **freezing drizzle
| + | |
| − | **[[dew]]
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| − | *solid precipitation
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| − | **[[snow]]
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| − | **[[snow pellets]]
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| − | **[[snow grains]]
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| − | **[[ice pellets]]
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| − | **frozen rain
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| − | **[[hail]]
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| − | **[[ice crystals]]
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| − | ** [[hoarfrost]]
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| − | ** [[atmospheric icing]]
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| − | ** [[glaze ice]]
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| − | *mixed precipitation
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| − | **in temperatures around 0 °C
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| − | |}
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| − | ** levitating particles
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| − | *** [[clouds]]
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| − | *** [[fog]]
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| − | *** BR (according to [[METAR]])
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| − | ** ascending particles (drifted by wind)
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| − | *** [[spindrift]]
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| − | *** ''stirred snow''
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| − | *'''according to occurrence'''
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| − | ** [[groundwater]]
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| − | ** [[meltwater]]
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| − | ** [[meteoric water]]
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| − | ** [[fresh water]]
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| − | ** [[mineral water]] – contains much minerals
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| − | ** [[brackish water]]
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| − | ** [[dead water]] – strange phenomenon which can occur when a layer of fresh or brackish water rests on top of more dense salt water, without the two layers mixing. It is dangerous for ship traveling.
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| − | ** [[seawater]]
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| − | ** [[brine]]
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| − | *'''according to uses'''
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| − | ** [[tap water]]
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| − | ** [[bottled water]]
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| − | ** [[drinking water]] or potable water – useful for everyday drinking, without fouling, it contains balanced minerals that are not harmful to health (see below)
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| − | ** [[purified water]], laboratory-grade, analytical-grade or reagent-grade water – water which has been highly purified for specific uses in science or engineering. Often broadly classified as Type I, Type II, or Type III, this category of water includes, but is not limited to the following:
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| − | ***[[distilled water]]
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| − | ***[[double distilled water]]
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| − | ***[[deionized water]]
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| − | *'''according to other features'''
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| − | ** [[soft water]] – contains less minerals
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| − | ** [[hard water]] – from underground, contains more minerals
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| − | ** [[distilled water]], [[double distilled water]], [[deionized water]] - contains no minerals
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| − | ** [[heavy water]] – made from heavy atoms of [[hydrogen]] - [[deuterium]]. It is in nature in normal water in very low concentration. It was used in construction of first [[Nuclear reactor technology|nuclear reactors]].
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| − | ** [[tritiated water]]
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| − | *'''according to [[microbiology]]'''
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| − | **[[drinking water]]
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| − | **[[wastewater]]
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| − | **[[stormwater]] or [[surface water]]
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| − | *'''according to religion'''
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| − | **[[holy water]]
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| − | == Chemical and physical properties ==
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| − | {|align="right" border="1" cellspacing="0" cellpadding="3" style="margin: 0 0 0 0.5em; background: #FFFFFF; border-collapse: collapse; border-color: #C0C090;"
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| − | ! {{chembox header}} | <big>[[Water (molecule)|Water]]</big>
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| − | |-
| + | |
| − | | 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.]]
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| − | Water is a necessary [[solvent]] for all known life, and<br>an abundant [[chemical compound|compound]] on the earth's surface.
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| − | |-
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| − | ! {{chembox header}} | Information and properties
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| − | |-
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| − | | [[Common name]]
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| − | | water
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| − | |-
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| − | | [[IUPAC name]]
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| − | | [http://www.acdlabs.com/iupac/nomenclature/93/r93_182.htm oxidane]
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| − | |-
| + | |
| − | | Alternative names
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| − | | aqua, [[dihydrogen monoxide]], <br>hydrogen hydroxide, ([[wikt:wikisaurus:water|more]])
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| − | |-
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| − | | [[Molecular formula]]
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| − | | H<sub>2</sub>O
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| − | | [[CAS number]]
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| − | | 7732-18-5
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| − | |-
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| − | | [[International Chemical Identifier|InChI]]
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| − | | InChI=1/H2O/h1H2
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| − | | [[Molar mass]]
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| − | | 18.0153 g/mol
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| − | | [[Density]] and [[Phase (matter)|phase]]
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| − | | 0.998 g/cm³ <small>(liquid at 20 °C, 1 atm)</small><br> 0.917 g/cm³ <small>(solid at 0 °C, 1 atm)</small>
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| − | |-
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| − | | [[Melting point]]
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| − | | 0 [[Celsius|°C]] (273.15 [[kelvin|K]]) (32 [[Fahrenheit|°F]])
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| − | |-
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| − | | [[Boiling point]]
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| − | | 99.974 °C (373.124 K) (211.95 °F)
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| − | |-
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| − | | [[Specific heat capacity]]
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| − | | 4.184 J/(g·K) <small>(liquid at 20 °C)</small>
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| − | |-
| + | |
| − | ! {{chembox header}} | [[Water (data page)|Supplementary data page]]
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| − | |-
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| − | | 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>
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| − | |-
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| − | |}
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| − | {{main|Water (molecule)}}
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| − | [[Image:3D model hydrogen bonds in water.jpg|left|thumb|model of [[hydrogen bond]]s between molecules of water]]
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| − | [[Image:Water droplet blue bg05.jpg|left|thumb|Impact from a water drop causes an upward "rebound" jet surrounded by circular [[capillary wave]]s.]]
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| − | <!-- Image with unknown copyright status removed: [[Image:Pearl_droplet.jpg|thumb|left|Droplet frozen by flash. www.liquidartgallery.com]] -->
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| − | [[Image:Spider web Luc Viatour.jpg|thumb|left|[[Dew]] drops adhering to a [[spider web]]]]
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| − | [[Image:Capillarity.svg|left|thumb|capillary action of water compared to [[Mercury (element)|mercury]]]]
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| − | 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.
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| − | The major chemical and physical properties of water are:
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| − | | + | |
| − | * Water is a tasteless, odorless liquid at [[standard conditions|ambient temperature and pressure]]. The [[color of water]] and ice are, intrinsically, a very light blue hue, although water appears colorless in small quantities. Ice also appears colorless, and water vapor is essentially invisible as a gas.<ref>{{cite journal|last=Braun|first=Charles L.|coauthors=Sergei N. Smirnov|title=Why is water blue?|journal=J. Chem. Educ.|volume=70|issue=8|pages=612|date=1993|url=http://www.dartmouth.edu/~etrnsfer/water.htm|format=HTML}}</ref>
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| − | | + | |
| − | * Water is [[transparency (optics)|transparent]], and thus [[aquatic plant]]s can live within the water because sunlight can reach them. Only strong UV light is slightly [[Uv#Blockers and absorbers|absorbed]].
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| − | | + | |
| − | * Water is a liquid under standard conditions.
| + | |
| − | | + | |
| − | * Since oxygen has a higher [[electronegativity]] than hydrogen, water is a [[polar molecule]]. The oxygen has a slight negative charge while the hydrogens have a slight positive charge giving the article a strong effective [[dipole]] [[Electrical dipole moment|moment]]. The interactions between the different dipoles of each molecule cause a net attraction force associated with water's high amount of [[surface tension]].
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| − | | + | |
| − | * Another very important force that causes the water molecules to stick to one another is the [[hydrogen bond]].
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| − | | + | |
| − | * The boiling point of water (and all other liquids) is directly related to the barometric pressure. For example, on the top of [[Mt. Everest]] water boils at about {{convert|68|°C}}, compared to {{convert|100|°C}} at [[sea level]]. Conversely, water deep in the ocean near geothermal vents can reach temperatures of hundreds of degrees and remain liquid.
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| − | | + | |
| − | * Water sticks to itself. Water has a high [[surface tension]] caused by the strong [[cohesion]] between water molecules because it is [[polar molecule|polar]]. The apparent elasticity caused by surface tension drives the [[capillary wave]]s.
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| − | | + | |
| − | * Water also has high [[adhesion]] properties because of its polar nature.
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| − | | + | |
| − | * [[Capillary action]] refers to the tendency of water to move up a narrow tube against the force of [[gravity]].
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| − | | + | |
| − | * 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 (chemistry)|salt]]s, [[sugar]]s, [[acid]]s, [[alkali]]s, and some [[gas]]es: especially [[oxygen]], [[carbon dioxide]] ([[carbonation]]), 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.
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| − | | + | |
| − | * All the major components in cells ([[protein]]s, [[DNA]] and [[polysaccharide]]s) are also dissolved in water.
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| − | * Pure water has a ''low'' [[electrical conductivity]], but this increases significantly upon solvation of a small amount of ionic material such as [[sodium chloride]].
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| − | * 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.
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| − | * The maximum [[density]] of water is at {{convert|3.98|°C}}. Water becomes even less dense upon freezing, expanding 9%. This causes an unusual phenomenon: ice floats upon water, and so water organisms can live inside a partly frozen pond because the water on the bottom has a temperature of around {{convert|4|°C}}.
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| − | * 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. As a gas, water vapor is completely [[miscible]] with air.
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| − | * Water forms an [[azeotrope]] with many other solvents.
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| − | [[Image:Label for dangerous goods - class 4.3.svg|right|thumb|[[European Agreement concerning the International Carriage of Dangerous Goods by Road|ADR]] [[Dangerous goods|label]] for transporting goods dangerously reactive with water]]
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| − | * Some substances ([[sodium]], [[lithium]], [[calcium]], [[potassium]]) emit a flammable gas (hydrogen) when wet, or react violently with water.
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| − | == Distribution of water in nature ==
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| − | ===Water in the Universe===
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| − | 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 observed is quickly produced in this warm dense gas.<ref>Gary Melnick, [[Harvard-Smithsonian Center for Astrophysics]] and David Neufeld, [[Johns Hopkins University]] quoted in:
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| − | {{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}}
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| − | {{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}}
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| − | {{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)
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| − | </ref>
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| − | Water has been detected in [[interstellar cloud]]s within our [[galaxy]], the [[Milky Way]]. It is believed that water exists in abundance in other galaxies too, because its components, [[hydrogen]] and [[oxygen]], are among the most abundant elements in the universe. Interstellar clouds eventually condense into [[solar nebula]]e and [[solar system]]s, such as ours.
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| − | Water vapor is on:
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| − | * [[Mercury (planet)|Mercury]] - 3.4% in the atmosphere
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| − | * [[Venus]] - 0.002% in the atmosphere
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| − | * [[Earth]] - trace in the atmosphere (varies with climate)
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| − | * [[Mars]] - 0.03% in the atmosphere
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| − | * [[Jupiter]] - 0.0004% in the atmosphere
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| − | * [[Saturn]] - in [[volatiles|ices]] only
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| − | * [[Enceladus (moon)|Enceladus]] (moon of Saturn) - 91% in the atmosphere
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| − | * [[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>
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| − | Liquid water is on:
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| − | * Earth - 71% of surface
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| − | | + | |
| − | Strong evidence suggests that liquid water is present just under the surface of Saturn's moon [[Enceladus (moon)|Enceladus]]. Probably some liquid water is on [[Europa (moon)|Europa]].
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| − | Water ice is on:
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| − | * Earth - mainly on [[ice sheet]]s
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| − | * polar ice caps on Mars
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| − | * [[Titan (moon)|Titan]]
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| − | * [[Europa (moon)|Europa]]
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| − | * [[Enceladus (moon)|Enceladus]]
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| − | Probability or possibility of distribution of water ice is at: [[lunar ice]] on the Moon, [[Ceres (dwarf planet)]], [[Tethys (moon)]]. Ice is probably in internal structure of [[Uranus]], [[Neptune]], and [[Pluto]] and on [[comet]]s.
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| − | ===Water and habitable zone===
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| − | [[Image:Habitable zone-en.svg|thumb|450px|right|The [[Solar System]] along center row range of possible [[habitable zone]]s of varying size stars.]]
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| − | The existence of liquid water, and to a lesser extent its gaseous and solid forms, on Earth is vital to the existence of [[Organism|life on Earth]] as we know it. The Earth is located in the [[habitable zone]] of the [[solar system]]; if it were slightly closer to or further from the [[Sun]] (about 5%, or 8 million kilometres 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].
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| − | </ref>
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| − | 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]]).
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| − | 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]]''.
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| − | 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.<!-- This refrence or common external link does not work now [http://www.cnn.com/2007/TECH/space/05/16/odd.exoplanet.reut/index.html]-->
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| − | | + | |
| − | There are various theories about [[origin of water on Earth]].
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| − | ==Water on Earth==
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| − | {{Main|Hydrology|Water distribution on Earth}}
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| − | [[Image:The Earth seen from Apollo 17.jpg|right|thumb|Water covers 71% of the Earth's surface; the [[ocean]]s contain 97.2% of the 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]].]]
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| − | 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]].
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| − | The collective mass of water found on, under, and over the surface of a planet is called [[hydrosphere]]. Earth's approximate water volume (the total water supply of the world) is 1 360 000 000 km³ (326 000 000 mi³). Of this volume:
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| − | * 1 320 000 000 km³ (316 900 000 mi³ or 97.2%) is in the [[sea water|oceans]].
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| − | * 25 000 000 km³ (6 000 000 mi³ or 1.8%) is in [[glaciers]], [[ice caps]] and [[ice sheets]].
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| − | * 13 000 000 km³ (3,000,000 mi³ or 0.9%) is [[groundwater]].
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| − | * 250 000 km³ (60,000 mi³ or 0.02%) is [[fresh water]] in lakes, inland seas, and rivers.
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| − | * 13 000 km³ (3,100 mi³ or 0.001%) is atmospheric water vapor at any given time.
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| − | Groundwater and fresh water are useful or potentially useful to humans as [[water resources]].
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| − | 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 phases. It also exists as groundwater in [[aquifer]]s.
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| − | The most important geological processes caused by water are: [[Weathering#Chemical weathering|chemical weathering]], [[Erosion#Water erosion|water erosion]], water [[sediment]] transport and sedimentation, [[mudflow]]s, [[Erosion#Ice erosion|ice erosion]] and sedimentation by glacier.
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| − | === Water cycle ===
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| − | {{Main|Water cycle}}
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| − | [[Image:Water cycle.png|right|thumb|[[water cycle]]]]
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| − | The [[water cycle]] (known scientifically as the '''hydrologic cycle''') refers to the continuous exchange of water within the [[hydrosphere]], between the [[Earth atmosphere|atmosphere]], [[soil]] water, [[surface water]], [[groundwater]], and [[plant]]s.
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| − | Water moves perpetually through each of these regions in the ''[[water cycle]]'' consisting of following transfer processes:
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| − | *[[evaporation]] from oceans and other water bodies into the air and [[transpiration]] from land plants and animals into air.
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| − | *[[precipitation (meteorology)|precipitation]], from water vapor condensing from the air and falling to earth or ocean.
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| − | *[[runoff (water)|runoff]] from the land usually reaching the [[sea]].
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| − | 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.
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| − | Water runoff often collects over [[Drainage basin|watershed]]s flowing into rivers. A mathematical model used to simulate river or stream flow and calculate water quality parameters is [[hydrological transport model]]. Some of water 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. 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 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.
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| − | ===Fresh water storage===
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| − | {{Main|Water resources}}
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| − | Some runoff water is trapped for periods, for example in lakes.
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| − | At high altitude, during winter, and in the far north and south, snow collects in ice caps, snow pack and glaciers.
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| − | 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.
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| − | 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.
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| − | ===Tides===
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| − | {{imageframe
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| − | |width=240
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| − | |content=[[Image:Bay of Fundy High Tide.jpg|120px]][[Image:Bay of Fundy Low Tide.jpg|120px]]
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| − | |caption=High tide (left) and low tide (right).
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| − | }}
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| − | {{main|Tide}}
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| − | '''[[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.
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| − | 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.
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| − | == Effects on life ==
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| − | [[Image:Oasis in Lybia.JPG|thumb|An [[oasis]] is an isolated [[water source]] with vegetation in desert]]
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| − | [[Image:Blue Linckia Starfish.JPG|thumb|right|Some of the [[biodiversity]] of a [[coral reef]]]]
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| − | [[Image:Water Flash.JPG|thumb|right|Water reflecting light in [[Crissy Field]]]]
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| − | 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.
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| − | 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).
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| − | 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.
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| − | For example a cell of ''[[Escherichia coli]]'' contains 70% of water, a human body 60-70%, plant body up to 90% and the body of an adult [[jellyfish]] is made up of 94–98% water.
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| − | ===Aquatic life forms===
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| − | {{Main|Hydrobiology|Aquatic plant}}
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| − | [[Image:Diatoms through the microscope.jpg|thumb|left|Some marine [[diatom]]s - a key [[phytoplankton]] group]]
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| − | Earth's 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 [[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]].
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| − | Aquatic animals 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 mammal]]s, such as dolphins, whales, [[otter]]s, and [[pinniped|seals]] need to surface periodically to breathe air. Smaller life forms are able to absorb oxygen through their skin.
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| − | ==Effects on human civilization==
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| − | [[Image:Longwood Gardens-Italian Garden.jpg|thumb|right| Water [[Fountain]]]]
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| − | 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.
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| − | === Health and pollution===
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| − | [[Image:Field_Trip-_water_sampling.jpg|thumb|[[Environmental Scientist]] sampling water.]]
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| − | Water fit for [[human]] consumption is called [[drinking water]] or [[potable water]]. Water that is not potable can be made potable by filtration or 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).
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| − | 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 and over 1 billion without access to adequate sanitation. 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, 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.
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| − | In the developing world, 90% of all [[wastewater]] still goes untreated into local rivers and streams.<ref>{{cite book |title=Environmentally Sound Technology for Wastewater and Stormwater Management: An International Source Book |author=UNEP International Environment |year=2002 |publisher=IWA Publishing |isbn=1843390086 }}</ref> 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.<ref>{{cite book |title=Climate Change and Developing Countries |last=Ravindranath |first=Nijavalli H. |coauthors=Jayant A. Sathaye |year=2002 |publisher=Springer |isbn=1402001045 }}</ref> The strain not only affects surface freshwater bodies like rivers and lakes, but it also degrades groundwater resources.
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| − | ===Human uses===
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| − | ====Agriculture====
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| − | [[Image:SiphonTubes.JPG|thumb|right|[[irrigation]] of field crops]]
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| − | The most important use of water in [[agriculture]] is for an [[irrigation]] and irrigation is key component to produce enough food. Irrigation takes up to 90% of water withdrawn in some developing countries.<ref>[http://www.wbcsd.org/includes/getTarget.asp?type=d&id=MTYyNTA WBCSD Water Faacts & Trends]</ref>
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| − | ====As a scientific standard====
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| − | 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 to the temperature of the melting ice."<ref>''[http://smdsi.quartier-rural.org/histoire/18germ_3.htm Decree relating to the weights and measurements]''</ref> For practical purposes though, a metallic reference standard was required, one thousand times more massive, the [[kilogram]]. Work was therefore commissioned to determine precisely how massive one [[Litre|liter]] of water was. In spite of the fact that the decreed definition of the gram specified water at 0 °C—a highly stable ''temperature'' point—the scientists chose to redefine the standard and to perform their measurements at the most stable ''density'' point: the temperature at which water reaches maximum density, which was measured at the time as 4 °C.<ref>''[http://histoire.du.metre.free.fr/fr/index.htm here L'Histoire Du Mètre, La Détermination De L'Unité De Poids]''</ref>
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| − | | + | |
| − | The [[Kelvin temperature scale]] of the SI system is based on the [[triple point]] of water. The scale is a more accurate development of the Celsius temperature scale, which is defined by the [[boiling point]] (100 °C) and [[melting point]] (0 °C) of water.
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| − | | + | |
| − | Natural water consists mainly of the isotopes hydrogen-1 and oxygen-16, but there is also small quantity of heavier 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, a standard water called [[Vienna Standard Mean Ocean Water]] is defined as the standard water.
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| − | ====For drinking====
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| − | [[Image:Humanitarian aid OCPA-2005-10-28-090517a.jpg|thumb|right|A young girl drinking [[bottled water]].]]
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| − | {{main|Drinking water}}
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| − | The [[human]] body is anywhere from 55% to 78% water depending on body size.<ref> [http://www.madsci.org/posts/archives/2000-05/958588306.An.r.html Re: What percentage of the human body is composed of water?] Jeffrey Utz, M.D., The MadSci Network </ref> 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 advocates agree that 6–7 glasses of water (approximately 2 litres) 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> Medical literature favors a lower consumption, typically 1 liter of water for an average male, excluding extra requirements due to fluid loss from exercise or warm weather.<ref name=Rhoades_2003>{{cite book | author = Rhoades RA, Tanner GA | title = Medical Physiology | publisher = Lippincott Williams & Wilkins | edition = 2nd ed. | location = Baltimore | year = 2003 | isbn = 0781719364 }}</ref> 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 "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>
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| − | An 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]]—who recommend that, on average, women consume 2.2 litres and men 3.0 litres—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 Water: How much should you drink every day? - MayoClinic.com<!-- Bot generated title -->]</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.
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| − | [[Image:D-P005 Kein Trinkwasser.svg|thumb|right|[[Hazard symbol]] for ''No drinking water'']]
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| − | 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. <ref>{{cite book
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| − | | last = Maton
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| − | | first = Anthea
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| − | | authorlink =
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| − | | coauthors = Jean Hopkins, Charles William McLaughlin, Susan Johnson, Maryanna Quon Warner, David LaHart, Jill D. Wright
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| − | | title = Human Biology and Health
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| − | | publisher = Prentice Hall
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| − | | date = 1993
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| − | | location = Englewood Cliffs, New Jersey, USA
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| − | | pages =
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| − | | url =
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| − | | doi =
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| − | | id =
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| − | | isbn = 0-13-981176-1}}</ref>
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| − | The single largest freshwater resource suitable for drinking is [[Lake Baikal]] in Siberia, which has a very low [[salt]] and [[calcium]] content and is very clean.
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| − | ====As a dissolving agent or solvent ====
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| − | [[Solvation|Dissolving]] (or [[suspension (chemistry)|suspending]]) is used to wash everyday items such as the human body, clothes, floors, cars, food, and pets. Also, [[human waste]]s are carried by water in the [[sewage system]]. Its use as a cleaning solvent consumes most of water in industrialized countries.
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| − | Water can facilitate the chemical processing of [[wastewater]]. An aqueous environment can be favourable to the breakdown of pollutants, due to the ability to gain an homogenous solution that is pumpable and flexible to treat. Aerobic treatment can be used by applying oxygen or air to a solution reduce the reactivity of substances within it.
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| − | Water also facilitates biological processing of [[waste]] that have been dissolved within it. Microorganisms that live within water can access dissolved wastes and can feed upon them breaking them down into less polluting substances. [[Reedbed]]s and [[anaerobic digester]]s are both examples of biological systems that are particularly suited to the treatment of effluents.
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| − | Typically from both chemical and biological treatment of wastes, there is often a solid residue or cake that is left over from the treatment process. Depending upon its constituent parts, this 'cake' may be dried and spread on land as a fertilizer if it has beneficial properties, or alternatively disposed of in [[landfill]] or [[incinerated]].
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| − | Water is the most abundant molecule in organisms.Fruits shrink when they are dried because they consist primarly of water.
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| − | ====As a heat transfer fluid====
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| − | [[Image:Kookwekker1268.JPG|thumb|ice used for cooling]]
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| − | Water and steam are used as heat transfer fluids in diverse heat exchange systems, due to its availability and high heat capacity, both as a coolant and for heating. Cool water may even be naturally available from a lake or the sea. Condensing [[steam]] is a particularly efficient heating fluid because of the large heat of vaporization. A disadvantage is that water and steam are somewhat corrosive. In almost all electric power plants, water is the coolant, which vaporizes and drives steam [[turbine]]s to drive generators.
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| − | In the nuclear industry, water can also be used as a [[neutron moderator]]. In a [[pressurized water reactor]], water is both a coolant and a moderator. This provides a passive safety measure, as removing the water from the reactor also slows the nuclear reaction down.
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| − | ====Extinguishing fires====
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| − | [[Image:MH-60S Helicopter dumps water onto Fire.jpg|right|thumb|Water is used for [[fire fighting|fighting]] [[wildfire]]s.]]
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| − | Water has a high heat of vaporization and is relatively inert, which makes it a good [[Fire fighting#Use of water|fire extinguishing]] fluid. The evaporation of water carries heat away from the fire. However, water cannot be used to fight fires of electric equipment, because impure water is electrically conductive, or of oils and organic solvents, because they float on water and the explosive boiling of water tends to spread the burning liquid.
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| − | | + | |
| − | Decomposition of water may have played a role in the [[Chernobyl disaster]]. Initially, cooling of the incandescent reactor was attempted, but the result was an explosion, when the extreme heat caused water to flash into steam, thus leading to a [[steam explosion]]; it may also have decomposed water into hydrogen and oxygen, which subsequently exploded.
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| − | ====Chemical uses====
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| − | Organic reactions are usually [[quench]]ed with water or a water solution of a suitable acid, base or buffer. Water is generally effective in removing inorganic salts. In inorganic reactions, water is a common solvent. In organic reactions, it is usually not 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 reaction]]s by water has been observed. [[Supercritical water]] has recently been a topic of research. Oxygen-saturated supercritical water combusts organic pollutants efficiently.
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| − | ====Recreation====
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| − | {{Main|Water sport (recreation)}}
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| − | Humans use water for many recreational purposes, as well as for exercising and for sports. Some of these include [[swimming]], [[waterskiing]], [[boating]], and [[diving]]. In addition, some sports, like [[ice hockey]] and [[ice skating]], are played on ice.
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| − | Lakesides, beaches and [[waterpark]]s 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]]s 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.
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| − | People may also use water for [[play fighting]] such as with [[snowball]]s, [[water gun]]s or [[water balloon]]s.
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| − | They may also make fountains and use water in their public or private decorations.
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| − | ====Water industry====
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| − | {{Main|Water industry|:Category:Water supply and sanitation by country}}
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| − | [[Image:Water carrier.jpg|right|thumb|220px|A water-carrier in India,1882. In many places where running water is not available, water has to be transported by people.]]
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| − | The [[water industry]] provides [[drinking water]] and [[wastewater]] services (including [[sewage treatment]]) to households and industry.
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| − | [[Image:TapWater-china.JPG|thumb|left|A manual water [[pump]] in China]]
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| − | [[Image:Usine Bret MG 1648.jpg|left|thumb|[[water purification]] facility]]
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| − | [[Image:Reflection.JPG|Left|250px|thumb|Water used in landscaping.]]
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| − | [[Water supply]] facilities includes for example [[water well]]s [[cistern]]s for [[rainwater harvesting]], [[water supply network]], [[water purification]] facilities, [[water tank]]s, [[water tower]]s, [[water pipe]]s including old [[aqueduct]]s. [[Atmospheric water generator]] is in development.
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| − | 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.
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| − | 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]].
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| − | 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 [[Water conservation|conserve fresh water resources]].
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| − | 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]].
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| − | Wastewater facilities are [[sewer]]s and [[wastewater treatment plant]]s. Another way to remove pollution from [[surface runoff]] water is [[bioswale]].
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| − | ====Industrial applications====
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| − | [[Image:200407-sandouping-sanxiadaba-4.med.jpg|right|thumb|[[Three Gorges Dam]] is the [[List of the largest hydoelectric power stations|largest hydro-electric power station]]]]
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| − | 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 sun. Heat from the sun evaporates water, which condenses as rain in higher altitudes, from where it flows down.
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| − | 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. It is also used in the cooling of machinery to prevent over-heating, or prevent saw blades from over-heating.
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| − | 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 ([[water pollution|chemical pollution]]) and discharged coolant water (thermal pollution). Industry requires pure water for many applications and utilizes a variety of [[water purification|purification]] techniques both in water supply and discharge.
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| − | ====Food processing====
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| − | [[Image:Cuisson des pates.jpg|thumb|[[Water]] can be used to cook foods such as [[noodles]].]]
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| − | 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.
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| − | 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.
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| − | 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"/>
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| − | [[Boiling]], [[steaming]], and [[simmering]] are popular [[cooking]] methods that often require immersing food in water or its gaseous state, steam. While cooking water is used for [[dishwashing]] too.
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| − | ==Water politics and water crisis==
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| − | {{Main|Water politics|Water crisis}}
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| − | {{seealso|Water resources|Water law|Water right}}
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| − | [[Water politics]] is [[politics]] affected by water and [[water resources]]. 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. It causes health impacts and damage to biodiversity. The serious worldwide water situation is called [[water crisis]].
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| − | [[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 [[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]].
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| − | To halve, by 2015, the proportion of people without sustainable access to safe drinking water is one of the [[Millennium Development Goals]].
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| − | Fresh water — now more precious than ever in our history for its extensive use in agriculture, high-tech manufacturing, and energy production — is increasingly receiving attention as a resource requiring better [[water management]] and [[sustainable]] use.
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| − | Organizations concerned in water protection include [[International Water Association]] (IWA), [[WaterAid]], [[Water 1st]], [http://www.awra.org/ American Water Resources Association]. Water related conventions are [[United Nations Convention to Combat Desertification]] (UNCCD), [[International Convention for the Prevention of Pollution from Ships]], [[United Nations Convention on the Law of the Sea]] and [[Ramsar Convention]]. [[World Day for Water]] takes place at [[March 22]] and [[World Ocean Day]] at [[June 8]].
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| − | Water used in the production of a good or service is [[virtual water]].
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| − | ==Religion, philosophy, and literature==
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| − | [[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. -->
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| − | Water is considered a purifier in most religions. Major faiths that incorporate ritual washing ([[ablution]]) include [[Christianity]], [[Hinduism]], [[Rastafarianism]], [[Islam]], [[Shinto]], [[Taoism]], and [[Judaism]]. 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 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).
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| − | Some faiths use water especially prepared for religious purposes ([[holy water]] in some Christian denominations, ''[[Amrita]]'' 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 [[Jordan River]] (at least symbolically) in some Christian churches, the [[Zamzam Well]] in Islam and the River [[Ganges]] (among many others) in Hinduism.
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| − | 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>
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| − | The Ancient 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]].
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| − | 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]]''.
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| − | {{portalpar|Water|Drinking water.jpg}}
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| − | {{Portalpar|Sustainable development|Sustainable development.svg}}
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| − | {{sisterlinks|water}}
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| − | == References ==
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| − | {{reflist}}
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| − | == Further reading ==
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| − | * {{cite book | title=Principles of Food Chemistry 3rd Edition | year=1999 | author=John M. DeMan}}
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| − | * {{cite book | title= Essentials of Food Science 2nd Edition | year=2003 | author= Vickie A. Vaclavik and Elizabeth W. Christian}}
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| − | * OA Jones, JN Lester and N Voulvoulis, Pharmaceuticals: a threat to drinking water? ''TRENDS in Biotechnology'' 23(4): 163, 2005
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| − | * Franks, F (Ed), Water, A comprehensive treatise, Plenum Press, New York, 1972-1982
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| − | <!--* [http://twt.mpei.ac.ru/mas/worksheets/VTP_wsp.mcd Property of Water and Water Steam with Thermodynamic Surface]-->
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| − | * 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.)
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| − | * 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]
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| − | * Debenedetti, P. G., and Stanley, H. E.; "Supercooled and Glassy Water", ''Physics Today'' '''56''' (6), p. 40–46 (2003). [http://polymer.bu.edu/hes/articles/ds03.pdf Downloadable PDF (1.9 MB)]
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| − | * [[Water SA]]
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| − | === Water as a natural resource ===
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| − | * {{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]
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| − | * {{cite book | title=Last Oasis: Facing Water Scarcity | year=1997, second edition| first=Sandra | last=Postel | location=New York | publisher=Norton Press}}
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| − | * {{cite book | title=Water Rights: Scarce Resource Allocation, Bureaucracy, and the Environment | year=1991| author=Anderson}}
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| − | * {{cite book | title=Water: The Fate of Our Most Precious Resource | year=2003, revised edition| author=Marq de Villiers}}
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| − | * {{cite book | title=Water Wars: Drought, Flood, Folly and the Politics of Thirst | year=2002 | author=Diane Raines Ward}}
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| − | * {{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)
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| − | * {{cite book | title=Rivers of Empire: Water, Aridity, and the Growth of the American West | year=1992 | first=Donald | last=Worster}}
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| − | * {{cite book | title=Cadillac Desert: The American West and Its Disappearing Water | year=1993 | first=Marc | last=Reisner}}
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| − | * {{cite book | title=Blue Gold: The Fight to Stop the Corporate Theft of the World's Water | author=Maude Barlow, Tony Clarke | year=2003}}
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| − | * {{cite book | title=Water Wars: Privatization, Pollution, and Profit | author=Vandana Shiva | year=2002 | id=ISBN 0-7453-1837-1}}
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| − | * {{cite book | title=Troubled Water: Saints, Sinners, Truth And Lies About The Global Water Crisis | author=Anita Roddick, et al | year=2004}}
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| − | * {{cite book | title=The Holy Order of Water: Healing Earths Waters and Ourselves | author=William E. Marks | year=2001}}
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| − | {{Food chemistry}}
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Water is the most abundant material on the earth. Its chemical name is H2O, ant it consists of two hyrdrogen atoms and one oxygen atom joined with two covalent bonds. It sometimes falls from the sky, in a process that is usually referred to as rain.
