Editing Water (section)

==Properties==
{{Main|Properties of water}}
{{see also||Water (data page)|Water model}}
[[File:Water molecule (1).svg|thumb|right|A water molecule consists of two hydrogen atoms and one oxygen atom.]]
Water ({{chem2|H2O|auto=1}}) is a [[Chemical polarity|polar]] [[inorganic compound]]. At [[room temperature]] it is a [[taste]]less and [[odor]]less [[liquid]], nearly [[Transparency and translucency|colorless]] with a [[Color of water|hint of blue]].<!--please read the article before considering removing it.--> The simplest [[hydrogen chalcogenide]], it is by far the most studied chemical compound and is sometimes described as the "universal solvent" for its ability to dissolve more substances than any other liquid,<ref>{{Greenwood&Earnshaw2nd|page=620}}</ref><ref>{{cite web |title=Water, the Universal Solvent |url=http://water.usgs.gov/edu/solvent.html |website=[[USGS]] |access-date=27 June 2017 |archive-url=https://web.archive.org/web/20170709141251/https://water.usgs.gov/edu/solvent.html |archive-date=9 July 2017 |url-status=live }}</ref> though it is poor at dissolving nonpolar substances.<ref>{{Cite web |title=Solvent properties of water |url=https://www.khanacademy.org/science/biology/water-acids-and-bases/hydrogen-bonding-in-water/a/water-as-a-solvent |website=Khan Academy}}</ref> This allows it to be the "[[solvent]] of life":<ref>{{Cite book |title=Campbell Biology |last=Reece |first=Jane B. |date=2013 |publisher=[[Pearson Education|Pearson]] |isbn=978-0-321-77565-8 |edition=10th |page=48 }}</ref> indeed, water as found in nature almost always includes various dissolved substances, and special steps are required to obtain chemically [[pure water]]. Water is the only common substance to exist as a [[solid]], liquid, and [[gas]] in normal terrestrial conditions.<ref>{{Cite book |title=Campbell Biology |last=Reece |first=Jane B. |year=2013 |publisher=[[Pearson Education|Pearson]] |isbn=978-0-321-77565-8 |edition=10th |page=44 }}</ref>

===States===
[[File: States of Matter.svg|thumb|The three common states of matter]]
Along with ''oxidane'', ''water'' is one of the two official names for the chemical compound {{chem|H|2|O}};<ref>{{Cite book|url=http://old.iupac.org/publications/books/principles/principles_of_nomenclature.pdf |title=Principles of chemical nomenclature: a guide to IUPAC recommendations |last1=Leigh |first1=G. J. |last2 = Favre| first2 = H. A|last3 = Metanomski|first3 = W. V.|date=1998 |publisher=Blackwell Science|location=Oxford|oclc=37341352|isbn=978-0-86542-685-6|url-status=dead |archive-url=https://web.archive.org/web/20110726171925/http://old.iupac.org/publications/books/principles/principles_of_nomenclature.pdf |archive-date=26 July 2011}}</ref> it is also the liquid phase of {{chem|H|2|O}}.<ref name=pubchem>{{cite web |last1=PubChem |title=Water |url=https://pubchem.ncbi.nlm.nih.gov/compound/Water |publisher=National Center for Biotechnology Information |access-date=25 March 2020 |language=en |archive-date=3 August 2018 |archive-url=https://web.archive.org/web/20180803194841/https:m//pubchem.ncbi.nlm.nih.gov/compound/water |url-status=live }}</ref> The other two common [[states of matter]] of water are the solid phase, [[ice]], and the gaseous phase, [[water vapor]] or [[steam]]. The addition or removal of heat can cause [[phase transition]]s: [[freezing]] (water to ice), [[melting]] (ice to water), [[vaporization]] (water to vapor), [[condensation]] (vapor to water), [[sublimation (phase transition)|sublimation]] (ice to vapor) and [[Deposition (phase transition)|deposition]] (vapor to ice).<ref name=Belnay>{{cite web |last1=Belnay |first1=Louise |title=The water cycle |url=https://www.esrl.noaa.gov/gmd/education/info_activities/pdfs/Teacher_CTA_the_water_cycle.pdf |website=Critical thinking activities |publisher=Earth System Research Laboratory |access-date=25 March 2020 |archive-date=20 September 2020 |archive-url=https://web.archive.org/web/20200920152817/https://www.esrl.noaa.gov/gmd/education/info_activities/pdfs/Teacher_CTA_the_water_cycle.pdf |url-status=live }}</ref>

==== Density ====
{{See also|Frost weathering}}
Water is one of only a few common naturally occurring substances which, for some temperature ranges, become less [[density|dense]] as they cool, and the only known naturally occurring substance which does so while liquid. In addition it is unusual as it becomes significantly less [[density|dense]] as it freezes, though it is not unique in that respect.{{efn|Other substances with this property include [[bismuth]], [[silicon]], [[germanium]] and [[gallium]].<ref name=Oliveira/>}}

At 1&nbsp;atm pressure, it reaches its maximum density of {{convert|999.972|kg/m3|lb/cuft|sigfig=6|abbr=on}} at {{convert|3.98|°C}}.<ref>{{cite web |title=What is Density? |url=https://www.mt.com/sg/en/home/applications/Application_Browse_Laboratory_Analytics/Density/density-measurement.html |website=Mettler Toledo |access-date=11 November 2022 |archive-date=11 November 2022 |archive-url=https://web.archive.org/web/20221111064630/https://www.mt.com/sg/en/home/applications/Application_Browse_Laboratory_Analytics/Density/density-measurement.html |url-status=live }}</ref><ref name="NatureWaterStructure">{{cite journal |url=https://www.academia.edu/2230441 |title= Water – an enduring mystery |access-date=15 November 2016 |journal=Nature |volume=452 |issue=7185 |pages=291–2 |archive-url=https://web.archive.org/web/20161117211552/http://www.academia.edu/2230441/Water_Water_an_enduring_mystery |archive-date=17 November 2016 |url-status=live |bibcode=2008Natur.452..291B |last1=Ball |first1=Philip |year=2008 |doi=10.1038/452291a |pmid=18354466 |s2cid=4365814 |doi-access=free }}</ref>

Below that temperature, but above the freezing point of {{convert|0|°C}}, it expands becoming less dense until it reaches freezing point, reaching a density in its liquid phase of {{convert|999.8|kg/m3|lb/cuft|sigfig=6|abbr=on}}.

Once it freezes and becomes ice, it expands by about 9%, with a density of {{convert|917|kg/m3|lb/cuft|sigfig=4|abbr=on}}.<ref>{{cite book |last1=Kotz |first1=J. C. |last2=Treichel |first2=P. |last3=Weaver |first3=G. C. |year=2005 |title=Chemistry & Chemical Reactivity |publisher=Thomson Brooks/Cole |isbn=978-0-534-39597-1}}</ref><ref>{{cite book |last1=Ben-Naim |first1=Ariel |display-authors=etal |title=Alice's Adventures in Water-land |year=2011 |doi=10.1142/8068 |last2=Ben-Naim |first2=Roberta |isbn=978-981-4338-96-7}}</ref> This expansion can exert enormous pressure, bursting pipes and cracking rocks.<ref name="MM">{{cite journal |last1=Matsuoka |first1=N. |last2=Murton |first2=J. |title=Frost weathering: recent advances and future directions |journal=Permafrost and Periglacial Processes |volume=19 |issue= 2|pages=195–210 |year=2008 |doi=10.1002/ppp.620 |bibcode=2008PPPr...19..195M |s2cid=131395533 }}</ref> As a solid, it displays the usual behavior of contracting and becoming more dense as it cools. These unusual thermal properties have important consequences for life on earth.

In a lake or ocean, water at {{cvt|4|C|F}} sinks to the bottom, and ice forms on the surface, floating on the liquid water. This ice insulates the water below, preventing it from freezing solid. Without this protection, most aquatic organisms residing in lakes would perish during the winter.<ref>{{cite web |last1=Wiltse |first1=Brendan |title=A Look Under The Ice: Winter Lake Ecology |url=https://www.ausableriver.org/blog/look-under-ice-winter-lake-ecology |website=Ausable River Association |access-date=23 April 2020 |archive-date=19 June 2020 |archive-url=https://web.archive.org/web/20200619081813/https://www.ausableriver.org/blog/look-under-ice-winter-lake-ecology |url-status=live }}</ref> In addition, this anomalous behavior is an important part of the [[thermohaline circulation]] which distributes heat around the planet's oceans.

==== Magnetism ====
Water is a [[Diamagnetism|diamagnetic]] material.<ref name="Chen-2010">{{Cite web|last=Chen|first=Zijun|date=21 April 2010|title=Measurement of Diamagnetism in Water|url=http://conservancy.umn.edu/handle/11299/90865|language=en-US|journal=|hdl=11299/90865 |access-date=8 January 2022|archive-date=8 January 2022|archive-url=https://web.archive.org/web/20220108015508/https://conservancy.umn.edu/handle/11299/90865|url-status=live}}</ref> Though interaction is weak, with superconducting magnets it can attain a notable interaction.<ref name="Chen-2010" />

==== Phase transitions ====
At a pressure of one [[Standard atmosphere (unit)|atmosphere]] (atm), ice melts or water freezes (solidifies) at {{cvt|0|C|}} and water boils or vapor condenses at {{cvt|100|C|F}}. However, even below the boiling point, water can change to vapor at its surface by [[evaporation]] (vaporization throughout the liquid is known as [[boiling]]). Sublimation and deposition also occur on surfaces.<ref name=Belnay/> For example, [[frost]] is deposited on cold surfaces while [[snowflake]]s form by deposition on an aerosol particle or ice nucleus.<ref>{{cite web |last1=Wells |first1=Sarah |title=The Beauty and Science of Snowflakes |url=https://ssec.si.edu/stemvisions-blog/beauty-and-science-snowflakes |website=Smithsonian Science Education Center |access-date=25 March 2020 |language=en |date=21 January 2017 |archive-date=25 March 2020 |archive-url=https://web.archive.org/web/20200325185513/https://ssec.si.edu/stemvisions-blog/beauty-and-science-snowflakes |url-status=live }}</ref> In the process of [[freeze-drying]], a food is frozen and then stored at low pressure so the ice on its surface sublimates.<ref name=FreezeDrying>{{Cite book|title=Food processing technology: principles and practice|last=Fellows|first=Peter|date=2017|publisher=Woodhead Publishing/Elsevier Science|isbn=978-0-08-100523-1|edition=4th|location=Kent|pages=929–940|chapter=Freeze drying and freeze concentration|oclc=960758611}}</ref>

The melting and boiling points depend on pressure. A good approximation for the rate of change of the melting temperature with pressure is given by the [[Clausius–Clapeyron relation]]:

<math display="block"> \frac{d T}{d P} = \frac{T \left(v_\text{L}-v_\text{S}\right) }{L_\text{f}} </math>

where <math>v_\text{L}</math> and <math>v_\text{S}</math> are the [[molar volume]]s of the liquid and solid phases, and <math>L_\text{f}</math> is the molar [[latent heat]] of melting. In most substances, the volume increases when melting occurs, so the melting temperature increases with pressure. However, because ice is less dense than water, the melting temperature decreases.<ref name=Oliveira>{{cite book |last1=Oliveira |first1=Mário J. de |title=Equilibrium Thermodynamics |date=2017 |publisher=Springer |isbn=978-3-662-53207-2 |pages=120–124 |url=https://books.google.com/books?id=F8GRDgAAQBAJ&dq=denser+liquid+than+solid+phase+water+silicon+bismuth&pg=PA122 |access-date=26 March 2020 |language=en |archive-date=8 March 2021 |archive-url=https://web.archive.org/web/20210308003011/https://www.google.com/books/edition/Equilibrium_Thermodynamics/F8GRDgAAQBAJ?hl=en&gbpv=1&dq=denser+liquid+than+solid+phase+water+silicon+bismuth&pg=PA122&printsec=frontcover |url-status=live }}</ref> In glaciers, [[pressure melting point|pressure melting]] can occur under sufficiently thick volumes of ice, resulting in [[subglacial lake]]s.<ref>{{cite journal |last1=Siegert |first1=Martin J. |last2=Ellis-Evans |first2=J. Cynan |last3=Tranter |first3=Martyn |last4=Mayer |first4=Christoph |last5=Petit |first5=Jean-Robert |last6=Salamatin |first6=Andrey |last7=Priscu |first7=John C. |title=Physical, chemical and biological processes in Lake Vostok and other Antarctic subglacial lakes |journal=Nature |date=December 2001 |volume=414 |issue=6864 |pages=603–609 |doi=10.1038/414603a|pmid=11740551 |bibcode=2001Natur.414..603S |s2cid=4423510 }}</ref><ref>{{cite web |last1=Davies |first1=Bethan |title=Antarctic subglacial lakes |url=http://www.antarcticglaciers.org/glacier-processes/glacial-lakes/subglacial-lakes/ |website=AntarcticGlaciers |access-date=25 March 2020 |archive-date=3 October 2020 |archive-url=https://web.archive.org/web/20201003171536/http://www.antarcticglaciers.org/glacier-processes/glacial-lakes/subglacial-lakes/ |url-status=live }}</ref>

The Clausius-Clapeyron relation also applies to the boiling point, but with the liquid/gas transition the vapor phase has a much lower density than the liquid phase, so the boiling point increases with pressure.<ref>{{cite book |last1=Masterton |first1=William L. |last2=Hurley |first2=Cecile N. |title=Chemistry: principles and reactions |date=2008 |publisher=Cengage Learning |isbn=978-0-495-12671-3 |page=230 |edition=6th |url=https://books.google.com/books?id=teubNK-b2bsC&q=clapeyron%20equation%20boiling |access-date=3 April 2020 |archive-date=8 March 2021 |archive-url=https://web.archive.org/web/20210308080844/https://www.google.com/books/edition/Chemistry_Principles_and_Reactions/teubNK-b2bsC?hl=en&gbpv=1&bsq=clapeyron%20equation%20boiling |url-status=live }}</ref> Water can remain in a liquid state at high temperatures in the deep ocean or underground. For example, temperatures exceed {{convert|205|C}} in [[Old Faithful]], a geyser in [[Yellowstone National Park]].<ref>{{cite web |last1=Peaco |first1=Jim |title=Yellowstone Lesson Plan: How Yellowstone Geysers Erupt |location=Yellowstone National Park |publisher=U.S. National Park Service |url=https://www.nps.gov/yell/learn/education/classrooms/how-yellowstone-geysers-erupt.htm |access-date=5 April 2020 |language=en |archive-date=2 March 2020 |archive-url=https://web.archive.org/web/20200302093350/https://www.nps.gov/yell/learn/education/classrooms/how-yellowstone-geysers-erupt.htm |url-status=live }}</ref> In [[hydrothermal vent]]s, the temperature can exceed {{convert|400|C}}.<ref>{{cite news |last1=Brahic |first1=Catherine |title=Found: The hottest water on Earth |url=https://www.newscientist.com/article/dn14456-found-the-hottest-water-on-earth/ |access-date=5 April 2020 |work=New Scientist |archive-date=9 May 2020 |archive-url=https://web.archive.org/web/20200509103747/https://www.newscientist.com/article/dn14456-found-the-hottest-water-on-earth/ |url-status=live }}</ref>

At [[sea level]], the boiling point of water is {{convert|100|C}}. As atmospheric pressure decreases with altitude, the boiling point decreases by 1&nbsp;°C every 274&nbsp;meters. [[High-altitude cooking]] takes longer than sea-level cooking. For example, at {{convert|1524|m}}, cooking time must be increased by a fourth to achieve the desired result.<ref>{{cite web |last1=USDA Food Safety and Inspection Service |title=High Altitude Cooking and Food Safety |url=https://www.fsis.usda.gov/shared/PDF/High_Altitude_Cooking_and_Food_Safety.pdf |access-date=5 April 2020 |archive-date=20 January 2021 |archive-url=https://web.archive.org/web/20210120010850/https://www.fsis.usda.gov/shared/PDF/High_Altitude_Cooking_and_Food_Safety.pdf |url-status=dead }}</ref> Conversely, a [[pressure cooker]] can be used to decrease cooking times by raising the boiling temperature.<ref>{{cite web |title=Pressure Cooking – Food Science |url=https://www.exploratorium.edu/food/pressure-cooking |website=Exploratorium |language=en |date=26 September 2019 |access-date=21 April 2020 |archive-date=19 June 2020 |archive-url=https://web.archive.org/web/20200619044746/https://www.exploratorium.edu/food/pressure-cooking |url-status=live }}</ref> In a vacuum, water will boil at room temperature.<ref>{{cite news |last1=Allain |first1=Rhett |title=Yes, You Can Boil Water at Room Temperature. Here's How |url=https://www.wired.com/story/yes-you-can-boil-water-at-room-temperature-heres-how/ |access-date=5 April 2020 |magazine=Wired |date=12 September 2018 |language=en |archive-date=28 September 2020 |archive-url=https://web.archive.org/web/20200928044101/https://www.wired.com/story/yes-you-can-boil-water-at-room-temperature-heres-how/ |url-status=live }}</ref>

==== Triple and critical points ====
[[File:Phase diagram of water.svg|thumb|Phase diagram of water]]
On a pressure/temperature [[phase diagram]] (see figure), there are curves separating solid from vapor, vapor from liquid, and liquid from solid. These meet at a single point called the [[triple point]], where all three phases can coexist. The triple point is at a temperature of {{convert|273.16|K|C F}} and a pressure of {{convert|611.657|Pa|atm psi|sigfig=3}};<ref>{{cite journal |last1=Murphy |first1=D. M. |last2=Koop |first2=T. |title=Review of the vapour pressures of ice and supercooled water for atmospheric applications |journal=Quarterly Journal of the Royal Meteorological Society |date=1 April 2005 |volume=131 |issue=608 |page=1540 |doi=10.1256/qj.04.94 |bibcode=2005QJRMS.131.1539M |s2cid=122365938 |url=https://zenodo.org/record/1236243 |access-date=31 August 2020 |archive-date=18 August 2020 |archive-url=https://web.archive.org/web/20200818105335/https://zenodo.org/record/1236243 |url-status=live |doi-access=free }}</ref> it is the lowest pressure at which liquid water can exist. [[2019 revision of the SI|Until 2019]], the triple point was used to define the [[Kelvin|Kelvin temperature scale]].<ref>{{cite book |author=International Bureau of Weights and Measures |author-link=International Bureau of Weights and Measures |date=2006 |url=http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf |url-status=live |archive-url=https://web.archive.org/web/20170814094625/http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf |archive-date=14 August 2017 |title=The International System of Units (SI) |edition=8th |isbn=92-822-2213-6 |page=114|publisher=Bureau International des Poids et Mesures }}</ref><ref name=Brochure9_2019>{{cite web |title = 9th edition of the SI Brochure |publisher = BIPM |url = https://www.bipm.org/en/publications/si-brochure/ |date = 2019 |access-date = 20 May 2019 |df = dmy-all |archive-date = 19 April 2021 |archive-url = https://web.archive.org/web/20210419211921/https://www.bipm.org/en/publications/si-brochure |url-status = live }}</ref>

The water/vapor phase curve terminates at {{convert|647.096|K|C F}} and {{convert|22.064|MPa|psi atm}}.<ref name=IAPWS95>{{cite journal |last1=Wagner |first1=W. |last2=Pruß |first2=A. |title=The IAPWS Formulation 1995 for the Thermodynamic Properties of Ordinary Water Substance for General and Scientific Use |journal=Journal of Physical and Chemical Reference Data |date=June 2002 |volume=31 |issue=2 |page=398 |doi=10.1063/1.1461829}}</ref> This is known as the [[critical point (thermodynamics)|critical point]]. At higher temperatures and pressures the liquid and vapor phases form a continuous phase called a [[supercritical fluid]]. It can be gradually compressed or expanded between gas-like and liquid-like densities; its properties (which are quite different from those of ambient water) are sensitive to density. For example, for suitable pressures and temperatures it can [[miscibility|mix freely]] with [[Nonpolar molecule|nonpolar compounds]], including most [[organic compound]]s. This makes it useful in a variety of applications including high-temperature [[electrochemistry]] and as an ecologically benign solvent or [[catalysis|catalyst]] in chemical reactions involving organic compounds. In Earth's mantle, it acts as a solvent during mineral formation, dissolution and deposition.<ref>{{cite journal |last1=Weingärtner |first1=Hermann |last2=Franck |first2=Ernst Ulrich |title=Supercritical Water as a Solvent |journal=Angewandte Chemie International Edition |date=29 April 2005 |volume=44 |issue=18 |pages=2672–2692 |doi=10.1002/anie.200462468|pmid=15827975 }}</ref><ref>{{cite journal |last1=Adschiri |first1=Tadafumi |last2=Lee |first2=Youn-Woo |last3=Goto |first3=Motonobu |last4=Takami |first4=Seiichi |title=Green materials synthesis with supercritical water |journal=Green Chemistry |date=2011 |volume=13 |issue=6 |pages=1380 |doi=10.1039/c1gc15158d}}</ref>

==== Phases of ice and water ====
{{main|Ice}}
The normal form of ice on the surface of Earth is [[Ice Ih|ice I<sub>h</sub>]], a phase that forms crystals with [[Hexagonal crystal family|hexagonal symmetry]]. Another with [[Cubic crystal system|cubic crystalline symmetry]], [[Ice Ic|ice I<sub>c</sub>]], can occur in the upper atmosphere.<ref>{{cite journal |last1=Murray |first1=Benjamin J.|last2=Knopf |first2=Daniel A. |last3=Bertram |first3=Allan K. |year=2005|title=The formation of cubic ice under conditions relevant to Earth's atmosphere|journal=Nature|volume=434|pages=202–205|doi=10.1038/nature03403|pmid=15758996|issue=7030|bibcode=2005Natur.434..202M|s2cid=4427815}}</ref> As the pressure increases, ice forms other [[crystal structure]]s. As of 2024, twenty have been experimentally confirmed and several more are predicted theoretically.<ref>{{cite journal |last1=Salzmann |first1=Christoph G. |title=Advances in the experimental exploration of water's phase diagram |journal=The Journal of Chemical Physics |date=14 February 2019 |volume=150 |issue=6 |pages=060901 |doi=10.1063/1.5085163|pmid=30770019 |arxiv=1812.04333 |bibcode=2019JChPh.150f0901S |doi-access=free }}</ref> The eighteenth form of ice, [[ice XVIII]], a face-centred-cubic, superionic ice phase, was discovered when a droplet of water was subject to a shock wave that raised the water's pressure to millions of atmospheres and its temperature to thousands of degrees, resulting in a structure of rigid oxygen atoms in which hydrogen atoms flowed freely.<ref name="Sokol2021">{{cite magazine |url=https://www.wired.com/story/a-bizarre-form-of-water-may-exist-all-over-the-universe/ |title=A Bizarre Form of Water May Exist All Over the Universe |last=Sokol |first=Joshua |magazine=Wired |date=12 May 2019 |access-date=1 September 2021 |archive-url=https://web.archive.org/web/20190512130533/https://www.wired.com/story/a-bizarre-form-of-water-may-exist-all-over-the-universe/|archive-date=12 May 2019|url-status=live}}</ref><ref name="Millotetal2019">{{cite journal |last1=Millot |first1=M. |last2=Coppari |first2=F. |last3=Rygg |first3=J. R. |last4=Barrios |first4=Antonio Correa |last5=Hamel |first5=Sebastien |last6=Swift |first6=Damian C. |last7=Eggert |first7=Jon H. |year=2019 |title=Nanosecond X-ray diffraction of shock-compressed superionic water ice |journal=Nature |publisher=Springer |volume=569 |issue=7755 |pages=251–255 |doi=10.1038/s41586-019-1114-6 |pmid=31068720 |bibcode=2019Natur.569..251M |osti=1568026 |s2cid=148571419 |url=https://www.osti.gov/biblio/1568026 |access-date=5 March 2024 |archive-date=9 July 2023 |archive-url=https://web.archive.org/web/20230709172600/https://www.osti.gov/biblio/1568026 |url-status=live }}</ref> When sandwiched between layers of [[graphene]], ice forms a square lattice.<ref>{{cite journal |last1=Peplow |first1=Mark |title=Graphene sandwich makes new form of ice |journal=Nature |date=25 March 2015 |doi=10.1038/nature.2015.17175|s2cid=138877465 }}</ref>

The details of the chemical nature of liquid water are not well understood; some theories suggest that its unusual behavior is due to the existence of two liquid states.<ref name="NatureWaterStructure" /><ref>{{Cite journal |last1=Maestro |first1=L. M. |last2=Marqués |first2=M. I. |last3=Camarillo |first3=E. |last4=Jaque |first4=D. |last5=Solé |first5=J. García |last6=Gonzalo |first6=J. A. |last7=Jaque |first7=F. |last8=Valle |first8=Juan C. Del |last9=Mallamace |first9=F. |date=1 January 2016 |title=On the existence of two states in liquid water: impact on biological and nanoscopic systems |journal=International Journal of Nanotechnology |volume=13 |issue=8–9 |pages=667–677 |doi=10.1504/IJNT.2016.079670 |bibcode=2016IJNT...13..667M |s2cid=5995302 |archive-url=https://web.archive.org/web/20231115003311/http://pdfs.semanticscholar.org/fc61/afe755fe34c5e163daa3c402bb8f03c40d7f.pdf |archive-date=15 November 2023 |url-status=live |url=http://pdfs.semanticscholar.org/fc61/afe755fe34c5e163daa3c402bb8f03c40d7f.pdf |access-date=5 March 2024 }}</ref><ref>{{cite journal |first1=Francesco |last1=Mallamace |first2=Carmelo |last2=Corsaro |first3=H. Eugene |last3=Stanley |title=A singular thermodynamically consistent temperature at the origin of the anomalous behavior of liquid water|journal=Scientific Reports |date=18 December 2012 |volume=2 |issue=1 |page=993 |doi=10.1038/srep00993 |pmid=23251779 |pmc=3524791 |bibcode= 2012NatSR...2..993M}}</ref><ref>{{Cite journal |last1=Perakis |first1=Fivos |last2=Amann-Winkel |first2=Katrin |last3=Lehmkühler |first3=Felix |last4=Sprung |first4=Michael |last5=Mariedahl |first5=Daniel |last6=Sellberg |first6=Jonas A. |last7=Pathak |first7=Harshad |last8=Späh |first8=Alexander |last9=Cavalca |first9=Filippo|last10=Ricci|first10=Alessandro |last11=Jain |first11=Avni |last12=Massani |first12=Bernhard |last13=Aubree |first13=Flora |last14=Benmore |first14=Chris J. |last15=Loerting|author15-link=Thomas Loerting |first15=Thomas |last16=Grübel |first16=Gerhard |last17=Pettersson |first17=Lars G. M. |last18=Nilsson |first18=Anders |date=26 June 2017 |title=Diffusive dynamics during the high-to-low density transition in amorphous ice |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=13 |issue=8–9 |pages=667–677 |doi=10.1073/pnas.1705303114|pmc=5547632 |pmid=28652327|bibcode=2017PNAS..114.8193P |doi-access=free }}</ref>

===Taste and odor===
Pure water is usually described as tasteless and odorless, although [[humans]] have specific sensors that can feel the presence of water in their mouths,<ref name="pmid28553944">{{cite journal | vauthors = Zocchi D, Wennemuth G, Oka Y | title = The cellular mechanism for water detection in the mammalian taste system | journal = Nature Neuroscience | volume = 20 | issue = 7 | pages = 927–933 | date = July 2017 | pmid = 28553944 | doi = 10.1038/nn.4575 | s2cid = 13263401 | url = https://authors.library.caltech.edu/77104/6/nn.4575-S2.pdf | access-date = 27 January 2024 | archive-date = 5 March 2024 | archive-url = https://web.archive.org/web/20240305154837/https://s3.us-west-2.amazonaws.com/caltechauthors/99/15/d0ca-f08f-4315-b32e-c758f8dd1cc8/data?response-content-type=application/octet-stream&response-content-disposition=attachment%3B%20filename%3Dnn.4575-S2.pdf&X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIARCVIVNNAKP37N3MU/20240305/us-west-2/s3/aws4_request&X-Amz-Date=20240305T154835Z&X-Amz-Expires=60&X-Amz-SignedHeaders=host&X-Amz-Signature=c12110c390e86eaaada9c08cfa75fbc87beb2c703250bafb9358fda4dfc2acf4 | url-status = live }}</ref><ref name=emo>Edmund T. Rolls (2005). ''Emotion Explained''. Oxford University Press, Medical. {{ISBN|978-0198570035}}.</ref> and frogs are known to be able to smell it.<ref name=frog>R. Llinas, W. Precht (2012), ''Frog Neurobiology: A Handbook''. Springer Science & Business Media. {{ISBN|978-3642663161}}</ref> However, water from ordinary sources (including [[mineral water]]) usually has many dissolved substances that may give it varying tastes and odors. Humans and other animals have developed senses that enable them to evaluate the [[potability]] of water in order to avoid water that is too salty or [[putrid]].<ref name=candau>{{cite journal |last1=Candau |first1=Joël |year=2004 |title=The Olfactory Experience: constants and cultural variables |url=https://halshs.archives-ouvertes.fr/halshs-00130924 |journal=Water Science and Technology |volume=49 |issue=9 |pages=11–17 |access-date=28 September 2016 |archive-url=https://web.archive.org/web/20161002152229/https://halshs.archives-ouvertes.fr/halshs-00130924 |archive-date=2 October 2016 |url-status=live |doi=10.2166/wst.2004.0522 |pmid=15237601 |bibcode=2004WSTec..49...11C }}</ref>

===Color and appearance===
{{Main|Color of water}}
{{See also|Electromagnetic absorption by water}}
Pure water is [[Visual perception|visibly]] blue due to [[electromagnetic absorption by water|absorption]] of light in the region c. 600–800&nbsp;nm.<ref>{{cite journal |last=Braun |first=Charles L. |author2=Sergei N. Smirnov |title=Why is water blue? |journal=Journal of Chemical Education |volume=70 |issue=8 |page=612 |year=1993 |url=http://www.dartmouth.edu/~etrnsfer/water.htm |doi=10.1021/ed070p612 |bibcode=1993JChEd..70..612B |access-date=21 April 2007 |archive-url=https://web.archive.org/web/20120320060654/http://www.dartmouth.edu/~etrnsfer/water.htm |archive-date=20 March 2012 |url-status=live |url-access=subscription }}</ref> The color can be easily observed in a glass of tap-water placed against a pure white background, in daylight. The principal absorption bands responsible for the color are [[Overtone band|overtone]]s of the O–H stretching [[Molecular vibration|vibrations]]. The apparent intensity of the color increases with the depth of the water column, following [[Beer's law]]. This also applies, for example, with a swimming pool when the light source is sunlight reflected from the pool's white tiles.

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

In industry, [[near-infrared spectroscopy]] is used with aqueous solutions as the greater intensity of the lower overtones of water means that glass [[cuvette]]s with short path-length may be employed. To observe the fundamental stretching absorption spectrum of water or of an aqueous solution in the region around 3,500&nbsp;cm{{sup|−1}} (2.85&nbsp;μm)<ref>{{cite book |last1=Nakamoto |first1=Kazuo |title=Infrared and Raman Spectra of Inorganic and Coordination Compounds, Part A: Theory and Applications in Inorganic Chemistry |date=1997 |publisher=Wiley |location=New York |isbn=0-471-16394-5 |page=170 |edition=5th}}</ref> a path length of about 25&nbsp;μm is needed. Also, the cuvette must be both transparent around 3500&nbsp;cm{{sup|−1}} and insoluble in water; [[calcium fluoride]] is one material that is in common use for the cuvette windows with aqueous solutions.

The [[Raman spectroscopy|Raman-active]] fundamental vibrations may be observed with, for example, a 1&nbsp;cm sample cell.

[[Aquatic plant]]s, [[algae]], and other [[Photosynthesis|photosynthetic]] organisms can live in water up to hundreds of meters deep, because [[sunlight]] can reach them.
Practically no sunlight reaches the parts of the oceans below {{convert|1000|m}} of depth.

The [[refractive index]] of liquid water (1.333 at {{convert|20|C}}) is much higher than that of air (1.0), similar to those of [[alkane]]s and [[ethanol]], but lower than those of [[glycerol]] (1.473), [[benzene]] (1.501), [[carbon disulfide]] (1.627), and common types of glass (1.4 to 1.6). The refraction index of ice (1.31) is lower than that of liquid water.

=== Molecular polarity ===
[[File:Tetrahedral Structure of Water.png|thumb|Tetrahedral structure of water]]
In a water molecule, the hydrogen atoms form a 104.5° angle with the oxygen atom. The hydrogen atoms are close to two corners of a tetrahedron centered on the oxygen. At the other two corners are ''[[lone pairs]]'' of valence electrons that do not participate in the bonding. In a perfect tetrahedron, the atoms would form a 109.5° angle, but the repulsion between the lone pairs is greater than the repulsion between the hydrogen atoms.<ref>{{harvnb|Ball|2001|p=168}}</ref><ref>{{harvnb|Franks|2007|p=10}}</ref> The O–H bond length is about 0.096&nbsp;nm.<ref>{{cite web |title=Physical Chemistry of Water |url=https://msu.edu/course/css/850/snapshot.afs/teppen/physical_chemistry_of_water.htm |publisher=Michigan State University |access-date=11 September 2020 |archive-date=20 October 2020 |archive-url=https://web.archive.org/web/20201020055601/https://msu.edu/course/css/850/snapshot.afs/teppen/physical_chemistry_of_water.htm |url-status=live }}</ref>

Other substances have a tetrahedral molecular structure, for example [[methane]] ({{chem|C|H|4}}) and [[hydrogen sulfide]] ({{chem|H|2|S}}). However, oxygen is more [[electronegativity|electronegative]] than most other elements, so the oxygen atom has a negative partial charge while the hydrogen atoms are partially positively charged. Along with the bent structure, this gives the molecule an [[electrical dipole moment]] and it is classified as a [[polar molecule]].<ref>{{harvnb|Ball|2001|p=169}}</ref>

Water is a good polar [[solvent]], dissolving many [[salt (chemistry)|salts]] and [[hydrophilic]] organic molecules such as sugars and simple alcohols such as [[ethanol]]. Water also dissolves many gases, such as oxygen and [[carbon dioxide]]—the latter giving the fizz of [[carbonation|carbonated]] beverages, [[sparkling wine]]s and beers. In addition, many substances in living organisms, such as [[protein]]s, [[DNA]] and [[polysaccharide]]s, are dissolved in water. The interactions between water and the subunits of these biomacromolecules shape [[protein folding]], [[Base pairing|DNA base pairing]], and other phenomena crucial to life ([[hydrophobic effect]]).

Many organic substances (such as [[lipids|fats and oils]] and [[alkanes]]) are [[hydrophobic]], that is, insoluble in water. Many inorganic substances are insoluble too, including most metal [[oxide]]s, [[sulfide]]s, and [[silicate]]s.

===Hydrogen bonding===
{{See also|Chemical bonding of water}}
[[File:3D model hydrogen bonds in water.svg|thumb|Model of [[hydrogen bond]]s (1) between molecules of water]]

Because of its polarity, a molecule of water in the liquid or solid state can form up to four [[hydrogen bonds]] with neighboring molecules. Hydrogen bonds are about ten times as strong as the [[Van der Waals force]] that attracts molecules to each other in most liquids. This is the reason why the melting and boiling points of water are much higher than those of [[Hydrogen chalcogenide|other analogous compounds]] like hydrogen sulfide. They also explain its exceptionally high [[specific heat capacity]] (about 4.2 [[Joule|J]]/(g·K)), [[heat of fusion]] (about 333 J/g), [[heat of vaporization]] ({{nowrap|2257 J/g}}), and [[thermal conductivity]] (between 0.561 and 0.679 W/(m·K)). These properties make water more effective at moderating Earth's [[climate]], by storing heat and transporting it between the oceans and the atmosphere. The hydrogen bonds of water are around 23 kJ/mol (compared to a covalent O-H bond at 492 kJ/mol). Of this, it is estimated that 90% is attributable to electrostatics, while the remaining 10% is partially covalent.<ref>{{Cite journal |date=1 March 2000 |title=Compton scattering evidence for covalency of the hydrogen bond in ice|journal=Journal of Physics and Chemistry of Solids |volume=61 |issue=3 |pages=403–406 |doi=10.1016/S0022-3697(99)00325-X |last1=Isaacs |first1=E. D. |last2=Shukla |first2=A |last3=Platzman |first3=P. M. |last4=Hamann |first4=D. R. |last5=Barbiellini |first5=B. |last6=Tulk |first6=C. A. |bibcode=2000JPCS...61..403I}}</ref>

These bonds are the cause of water's high [[surface tension]]<ref>{{cite book |last1=Campbell |first1=Neil A. |first2=Brad |last2=Williamson |first3=Robin J. |last3=Heyden |title=Biology: Exploring Life |publisher=Pearson Prentice Hall |year=2006 |location=Boston |url=http://www.phschool.com/el_marketing.html |isbn=978-0-13-250882-7 |access-date=11 November 2008 |archive-url=https://web.archive.org/web/20141102041816/http://www.phschool.com/el_marketing.html |archive-date=2 November 2014 |url-status=live }}</ref> and capillary forces. The [[capillary action]] refers to the tendency of water to move up a narrow tube against the force of [[gravity]]. This property is relied upon by all [[vascular plant]]s, such as trees.{{Citation needed|date=August 2022}}

[[File:Heat capacity of water 2.jpg|thumb|upright=1.4|Specific heat capacity of water<ref>{{Cite web |title=Heat capacity water online |url=https://www.desmos.com/calculator/wicmrvrznj?lang=ru |access-date=3 June 2022 |website=Desmos |language=ru |archive-date=6 June 2022 |archive-url=https://web.archive.org/web/20220606020344/https://www.desmos.com/calculator/wicmrvrznj?lang=ru |url-status=live }}</ref>]]

===Self-ionization===
{{main|Self-ionization of water}}

Water is a weak solution of hydronium hydroxide—there is an equilibrium {{Nowrap|{{chem|2H|2|O}} ⇌ {{chem|H|3|O|+}} + {{chem|OH|-}}}}, in combination with solvation of the resulting [[hydronium]] and [[hydroxide]] ions.

===Electrical conductivity and electrolysis===
Pure water has a low [[electrical conductivity]], which increases with the [[dissolution (chemistry)|dissolution]] of a small amount of ionic material such as [[sodium chloride|common salt]].

Liquid water can be split into the [[Chemical element|elements]] hydrogen and oxygen by passing an electric current through it—a process called [[Electrolysis of water|electrolysis]]. The decomposition requires more energy input than the [[standard enthalpy of formation|heat released by the inverse process]] (285.8 kJ/[[mole (unit)|mol]], or 15.9 MJ/kg).<ref>{{cite journal |last=Ball |first=Philip |author-link=Philip Ball |title=Burning water and other myths |url=http://www.nature.com/news/2007/070910/full/070910-13.html |journal=News@nature |date=14 September 2007 |access-date=14 September 2007 |archive-url=https://web.archive.org/web/20090228054247/http://www.nature.com/news/2007/070910/full/070910-13.html |archive-date=28 February 2009 |url-status=live |doi=10.1038/news070910-13 |s2cid=129704116 |doi-access=free }}</ref>

===Mechanical properties===
Liquid water can be assumed to be incompressible for most purposes: its compressibility ranges from 4.4 to {{val|5.1|e=-10|u=Pa<sup>−1</sup>}} in ordinary conditions.<ref>{{cite journal |last1=Fine |first1=R. A. |last2=Millero |first2=F. J.|date=1973 |title=Compressibility of water as a function of temperature and pressure |volume=59 |issue=10 |page=5529 |journal=Journal of Chemical Physics |doi=10.1063/1.1679903 |bibcode=1973JChPh..59.5529F}}</ref> Even in oceans at 4&nbsp;km depth, where the pressure is 400 atm, water suffers only a 1.8% decrease in volume.<ref name=nave>{{cite web |title=Bulk Elastic Properties |last=Nave |first=R. |website=HyperPhysics |publisher=[[Georgia State University]] |url=http://hyperphysics.phy-astr.gsu.edu/hbase/hph.html |access-date=26 October 2007 |archive-url=https://web.archive.org/web/20071028155517/http://hyperphysics.phy-astr.gsu.edu/hbase/hph.html |archive-date=28 October 2007 |url-status=live }}</ref>

The [[viscosity]] of water is about 10{{sup|−3}} Pa·[[second|s]] or 0.01 [[Poise (unit)|poise]] at {{convert|20|C}}, and the [[speed of sound]] in liquid water ranges between {{convert|1400|and|1540|m/s}} depending on temperature. Sound travels long distances in water with little [[attenuation]], especially at low frequencies (roughly 0.03 [[decibel|dB]]/km for 1 k[[hertz|Hz]]), a property that is exploited by [[cetaceans]] and humans for communication and environment sensing ([[sonar]]).<ref name=NPLcalc>UK National Physical Laboratory, [http://resource.npl.co.uk/acoustics/techguides/seaabsorption/ Calculation of absorption of sound in seawater] {{Webarchive|url=https://web.archive.org/web/20161003014920/http://resource.npl.co.uk/acoustics/techguides/seaabsorption/ |date=3 October 2016 }}. Online site, last accessed on 28 September 2016.</ref>

===Reactivity===
Metallic elements which are more [[Electronegativity|electropositive]] than hydrogen, particularly the [[alkali metals]] and [[alkaline earth metals]] such as [[lithium]], [[sodium]], [[calcium]], [[potassium]] and [[Caesium|cesium]] displace hydrogen from water, forming [[hydroxide]]s and releasing hydrogen. At high temperatures, carbon reacts with steam to form [[carbon monoxide]] and hydrogen.{{citation needed|date=November 2023}}