2007-09-01T07:23:00.000-07:00

Brief commentary, analysis and links by Dr. Glen Barry
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June 6, 2007
Water the Next Carbon
I heard on the radio yesterday that water is the next carbon. The expansion of Coca-Cola's water conservation efforts would allegedly be an example. I guess this means its use and misuse effects human societies ability to exist, but anyone could have told you that the water crisis is at least as far advanced as climate change. This water conservation blog has largely been inactive. As we did site updates on our climate, rainforest and environment portals we chose to do them on the water site, but sadly before we had the staff and resources to maintain a running commentary on water policy and highlighting major developments, issues and actions. Well with the current fund-raiser doing well I am going to try to start blogging on water more frequently (which as the last post was months ago, should not be difficult) -- hopefully at least once or twice a week but regularly. If there are guest writers that would like to blog here let me know. This water site's news tracking, search engine and links directory remain top-notch. Ecological Internet would greatly appreciate donations to help generate content for the Water Conservation Portal. Just under $10K to raise! See you soon.
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January 22, 2007
World Running Out of Water
The world is running out of potable water and a major policy initiative to guarantee freshwater as a human right is required. In a most interesting article from the Guardian, Jeffery Sachs of the UN's Millennium Project notes the world simply has "no more rivers to take water from". And the near total lack of basic water policy for the future is noted, such as how are aquifers to be recharged and how to sustain ground water use? For some time I have thought that a major water shortage crisis [search] that ravishes millions may, even more so than climate change (though it may be the cause), galvanize the world to realize the extent to which the global biosphere teeters upon the edge of ruin. Then we may see the surge of personal lifestyle changes and policy prescriptions from governments and businesses adequate to achieve global ecological sustainability. The article notes that not only are China's and India's water supplies threatened but their food production as well. These "economic miracles" have largely been built upon the back of unsustainable water and other resource use - a deck of cards waiting to fall. In closing Sachs is quoted as making a point I have harked on for years, that "for the first time humans were shaping the environment rather than nature". Where does your water come from? What happens if it runs dry? What will you do, where will you go?
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December 21, 2006
Death for China's 20 Million Year Old River Goddess
It is likely the first big aquatic mammal has become extinct due to human activity. "For 20 million years, the white-fin dolphin, or baiji, swam China's longest river, the Yangtze. But a few years of breakneck development, overfishing and a massive increase in shipping have reduced sightings of this shy, graceful creature to zero." After 38 days of failure, Chinese scientists intend to continue their search for the rare Yangtze river dolphin [search]. The extinction of this nearly blind freshwater cetacean should indicate that humans must work harder to achieve greater species conservation. For far too long humanity has treated natural freshwater sources and other critical global ecosystems as waste dumps. If we do not stop, all life is at risk, and what is likely to remain are dandelions, rats and cockroaches, if that. As we enter deeply within the Earth's sixth great extinction event [search], destruction of ecosystems and human over-population and consumption make human extinction all the more likely.
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November 27, 2006
China's Water Shortage Extremely Severe
The whole Chinese economic miracle is an illusory, short-lived experiment in over-population, over-resource use and disregard for ecological systems and their limits in general. Nowhere is this more evident than the the extreme water shortage wracking the country. "Two-thirds of Chinese cities face water shortages... More than 400 cities had water shortages, with 100 of them 'in serious trouble, lacking enough water to support industry or daily life." A country that dumps "45 billion tonnes of untreated waste water pumped directly into lakes and rivers" can not expect to engineer their way out of a looming water crisis [search]. China's hyper-economic growth cannot be maintained. Their leadership has traded the Earth's long-term prospects for an orgy of production of consumer crap, most of which is not needed. No one can realistically deny China the right to develop. But failure to get a grasp on environmental issues ensures the Chinese nation will implode - taking much of the region if not the world with it. The rich must live simply - rejecting the throw away consumer society - so that developing countries can simply live. It's called sustainable equity.
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November 12, 2006
World's Water Woes Dangerous and Deadly
After years of being treated as disposal dumps and water for crops, The Earth's natural freshwater hydrological systems are failing. Australia's Murray River system [search] has run virtually dry after years of water mismanagement compounded by climate change. As water discharges into surrounding wetlands [more] are discontinued in order to continue profiligate irrigation in deserts, the river's riparian zone is effectively dying making river recovery unlikely even if some rains should return. And as highlighted before, in a world of plenty with trillions to spend on military weaponry, some 5,000 children a day are dying from water carried preventable diseases. "Nearly two million children a year die for want of clean water and proper sanitation while the world's poor often pay more for their water than people in Britain or the US." Where is the outrage at this entirely preventable tragedy? NOTE: Following site redesign we have not had time to be water blogging, but expect to now. Thank you for your patience.
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September 17, 2006
Investors Bet on Rising Costs for Scarce Water
Multi-national corporations already own the seeds from which comes our food, and the energy we need to power our lifes. It makes sense that they would make a play to control water, access to which is becoming dangerously scarce for many. Access to clean water and air is a basic human right. "According to United Nations estimates, one third of the world's population lives in areas with water shortages and 1.1 billion people lack access to safe drinking water." The privitization of water will lead to huge disparities in access and consumption of this precious and absolutely necessary commodity. Once the mega-corps own our water we will all be their serfs. Water conservation depends upon ending inefficient uses, restoring hydrological systems, and guaranteeing access - and a whole bunch of other challenging policies truly adequate to achieve ecological sustainability such as reducing human population.
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September 9, 2006
Great Lakes Water Diversion
A new book entitled "The Great Lakes Water Wars" warns of coming conflict over Great Lakes water resources in an increasingly parched world.
"His premise is that an era of warring over the Great Lakes [search] is under way -- and will intensify as the global water shortage worsens. The lakes' future and the region's way of life hang in the balance as leaders grapple with the challenge of preserving what amounts to nearly one-fifth of the world's fresh surface water. The book comes nine months after representatives of the eight Great Lakes states signed a compact to ban most diversions of water outside the drainage basin, require each state to regulate water use and establish a regional standard for large-scale water withdrawals."
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August 16, 2006
Water Crisis
The Earth is being buffetted by a variety of environmental catastrophes. As humanity slumbers largely thinking things are fine it is difficult to identify which major eco-crisis will be the first to cause widespread death and destruction, probably the only way average Joe's are going to stop and think about where their water, air and food come from. I would say there is a 50/50 chance that the water crisis will be the first to truly bite (the other of course being climate change). Water is the lubricant of life and we continue to over use it and crap into it wherever found. The media is reporting on a new WWF report on the water crisis.
Continue reading "Water Crisis" »
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July 28, 2006
Widespread Water Pollutant Found to Be Highly Toxic
The scientific evidence continues to grow that trichloroethylene (TCE), the most widespread industrial contaminant found in drinking water, can cause cancer in people. TCE is a solvent used in adhesives, paint and spot removers. The military uses it widely to clean airplanes and missiles, and has resisted for years greater restrictions upon its use. A new National Academy of Sciences report found the chemical is a possible cause of kidney cancer, reproductive and developmental damage, impaired neurological function and autoimmune disease. The fact that the chemical has been used so widely, and it has been so difficult to react to emerging scientific information regarding its toxicity, shows the extent to which toxic chemicals are routinely introduced without regard to human health. There are hundreds of toxics in our water (search) and environment which we do not fully understand their human and ecological impacts, much less their combined interactions. Humanity must move beyond introducing "wonder" chemicals into their habitat that they do not understand or need.
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June 21, 2006
ALERT: Water More Precious than Gold, Stop Chile's Pascua Lama Gold Mine
Take Action: Glacier gold mine will taint pristine valley with cyanide
Canadian-based Barrick Gold plans to soon launch a gold mine in a remote Chilean valley that will destroy regional water supplies and devastate local sustainable agricultural practices. The Pascua Lama mining project is 80 miles south-west of the Chilean city of Vallena, and involves mining a very rich field of gold and silver in the high mountains between Chile and Argentina at an altitude of over 4,500 metres. The proposed "Pascua Lama" mine will devastate community water rights and indigenous farmers - leading to the destruction of glaciers and contamination of the purest of water sources necessary for Chile's well-being.
As is typical for gold mining, the project will use cyanide and other toxic materials to extract small amounts of gold from huge volumes of mined ore. Toxic chemical waste including cyanide will be removed via drainage into nearby rivers, seriously polluting marvelously pure glacial fed rivers, and causing long-term environmental impacts for local peoples. In a first, glaciers abutting and partially covering the proposed mine will be destroyed, posing a threat to the ecosystem and further contaminating the source of local water supplies, seriously harming agriculture and quality of life in the region.
Continue reading "ALERT: Water More Precious than Gold, Stop Chile's Pascua Lama Gold Rainforest Portal
"H2O" and "HOH" redirect here. For other uses, see H2O (disambiguation) and HOH (disambiguation).
This article describes water from a scientific and technical perspective. See Water for its importance in sustaining life and humanity, and Water (disambiguation) for other uses.
Water (H2O)

General
Systematic name
Water
Other names
AquaHydrogen oxideHydrogen hydroxideHydrateOxidaneHydric acidDihydrogen monoxideHydroxyl acidDihydrogen oxideHydrohydroxic acidμ-Oxido dihydrogenLight Water
Molecular formula
HOH or H2O
Molar mass
18.01524 g·mol−1
Appearance
transparent, almostcolorless liquid witha slight hint of blue[1]
CAS number
[7732-18-5]
see also
Water (data page)
Properties
Density and phase
1000 kg·m−3, liquid (4 °C)917 kg·m−3, solid
Melting point
0 °C, 32 °F (273.15 K)[2]
Boiling point
100 °C, 212 °F (373.15 K)[2]
Triple point
273.16 K, 611.73 Pa
Critical point
647 K, 22.1 MPa
Specific heatcapacity (gas)
cp=1970 J·kg−1·K−1 @ 300 Kcv=1510 J·kg−1·K−1 @ 300 K[3]
Specific heatcapacity (liquid)
4186 J·kg−1·K−1
Specific heatcapacity (solid)
2060 J·kg−1·K−1
Acidity (pKa)
15.74~22
Basicity (pKb)
15.74
Viscosity
0.001 Pa·s at 20 °C
Surface Tension at 20 °C
72.86 mN·m−1
Structure
Molecular shape
non-linear bent
Point Group
C2v
Crystal structure
HexagonalSee ice
Dipole moment
1.85 D
Hazards
MSDS
External MSDS
Main hazards
see Dihydrogen monoxide hoax
NFPA 704

0
0
0

RTECS number
ZC0110000
Supplementary data page
Structure andproperties
n, εr, etc.
Thermodynamicdata
Phase behaviourSolid, liquid, gas
Spectral data
UV, IR, NMR, MS
Related compounds
Related solvents
acetone methanol
Related compounds
water vapor ice heavy water
Except where noted otherwise, data are given formaterials in their standard state (at 25 °C, 100 kPa)Infobox disclaimer and references
Water (H2O, HOH) is the most abundant molecule on Earth's surface, composing of about 70% of the Earth's surface as liquid and solid state in addition to being found in the atmosphere as a vapor. It is in dynamic equilibrium between the liquid and vapor states at standard temperature and pressure. At room temperature, it is a nearly colorless, tasteless, and odorless liquid. Many substances dissolve in water and it is commonly referred to as the universal solvent. Because of this, water in nature and in use is rarely clean, and may have some properties different than those in the laboratory. However, there are many compounds that are essentially, if not completely, insoluble in water. Water is the only common, pure substance found naturally in all three states of matter—for other substances, see Chemical properties.
Contents[hide]
1 Forms of water
1.1 Water in the Universe
1.2 Water on Earth
1.3 Water in industry
2 Physics and chemistry of water
2.1 Density of water and ice
2.2 Density of saltwater and ice
2.3 Compressibility
2.4 Triple point
2.5 Mpemba effect
2.6 Hot ice
2.7 Surface tension
2.8 Electrical properties
2.9 Dipolar nature of water
2.10 Water as a solvent
2.11 Amphoteric nature of water
2.12 Acidity in nature
2.13 Hydrogen bonding in water
2.14 Quantum properties of molecular water
3 History
4 Systematic naming
4.1 Systematic nomenclature and humor
5 See also
6 References
7 External links
//

[edit] Forms of water
See the Category:Forms of water
Water can take many forms. The solid state of water is commonly known as ice (while many other forms exist; see amorphous solid water); the gaseous state is known as water vapor (or steam, though this is actually incorrect, since steam is just condensing liquid water droplets), and the common liquid phase is generally taken as simply water. Above a certain critical temperature and pressure (647 K and 22.064 MPa), water molecules assume a supercritical condition, in which liquid-like clusters float within a vapor-like phase.
Heavy water is water in which the hydrogen is replaced by its heavier isotope, deuterium. It is chemically almost identical to normal water. Heavy water is used in the nuclear industry to slow down neutrons.

[edit] Water in the Universe
Water has been detected in interstellar clouds 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 nebulae and solar systems, such as ours. The initial water can then be found in comets, planets, dwarf planets, and their satellites. In our solar system, water, in ice form, has been found:
on the Moon,
on the planets Mercury, Mars, and Neptune,
on the dwarf planet Pluto,
on satellites of planets, such as Triton and Europa.
The liquid form of water is only known to occur on Earth, though strong evidence suggests that it is present just under the surface of Saturn's moon Enceladus.

[edit] Water on Earth
The water cycle (known scientifically as the hydrologic cycle) refers to the continuous exchange of water within the hydrosphere, between the atmosphere, soil water, surface water, groundwater, and plants.
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:
1 320 000 000 km3 (316 900 000 mi3 or 97.2%) is in the oceans.
25 000 000 km3 (6 000 000 mi3 or 1.8%) is in glaciers, ice caps and ice sheets.
13 000 000 km3 (3,000,000 mi3 or 0.9%) is groundwater.
250 000 km3 (60,000 mi3 or 0.02%) is fresh water in lakes, inland seas, and rivers.
13 000 km3 (3,100 mi3 or 0.001%) is atmospheric water vapor at any given time.
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 aquifers.
The boiling point of water is directly related to the barometric pressure. For example, on the top of Mt. Everest water boils at about 68 degrees Celsius, compared to 100 degrees at sea level. Conversely, water deep in the ocean near geothermal vents can reach temperatures of hundreds of degrees and remain liquid.

[edit] Water in industry
Water is also used in many industrial processes and machines, such as the steam turbine and heat exchanger, in addition to its use as a chemical solvent. Discharge of untreated water from industrial uses is pollution. Pollution includes discharged solutes (chemical pollution) and discharged coolant water (thermal pollution). Industry requires pure water for many applications and utilizes a variety of purification techniques both in water supply and discharge.

[edit] Physics and chemistry of water

[edit] Density of water and ice
The solid form of most substances is more dense than the liquid phase; thus, a block of pure solid substance will sink in a tub of pure liquid substance. But, by contrast, a block of common ice will float in a tub of water because solid water is less dense than liquid water. This is an extremely important characteristic property of water. At room temperature, liquid water becomes denser with lowering temperature, just like other substances. But at 4 °C, just above freezing, water reaches its maximum density, and as water cools further toward its freezing point, the liquid water, under standard conditions, expands to become less dense. The physical reason for this is related to the crystal structure of ordinary ice, known as hexagonal ice Ih. Water, gallium, bismuth, antimony and silicon are some of the few materials which expand when they freeze; most other materials contract. It should be noted however, that not all forms of ice are less dense than liquid water. For example HDA and VHDA are both more dense than liquid phase pure water. Thus, the reason that the common form of ice is less dense than water is a bit non-intuitive and relies heavily on the unusual properties inherent to the hydrogen bond.
Generally, water expands when it freezes because of its molecular structure, in tandem with the unusual elasticity of the hydrogen bond and the particular lowest energy hexagonal crystal conformation that it adopts under standard conditions. That is, when water cools, it tries to stack in a crystalline lattice configuration that stretches the rotational and vibrational components of the bond, so that the effect is that each molecule of water is pushed further from each of its neighboring molecules. This effectively reduces the density ρ of water when ice is formed under standard conditions.
The importance of this property cannot be overemphasized for its role on the ecosystem of Earth. For example, if water were more dense when frozen, lakes and oceans in a polar environment would eventually freeze solid (from top to bottom). This would happen because frozen ice would settle on the lake and riverbeds, and the necessary warming phenomenon (see below) could not occur in summer, as the warm surface layer would be less dense than the solid frozen layer below. It is a significant feature of nature that this does not occur naturally in the environment.
Nevertheless, the unusual expansion of freezing water (in ordinary natural settings in relevant biological systems), due to the hydrogen bond, from 4 °C above freezing to the freezing point offers an important advantage for freshwater life in winter. Water chilled at the surface increases in density and sinks, forming convection currents that cool the whole water body, but when the temperature of the lake water reaches 4 °C, water on the surface decreases in density as it chills further and remains as a surface layer which eventually freezes and forms ice. Since downward convection of colder water is blocked by the density change, any large body of fresh water frozen in winter will have the coldest water near the surface, away from the riverbed or lakebed. This accounts for various little known phenomena of ice characteristics as they relate to ice in lakes and "ice falling out of lakes" as described by early 20th century scientist Horatio D. Craft.
The following table gives the density of water in grams per cubic centimeter at various temperatures in degrees Celsius:[4]
Temp (°C)
Density (g/cm3)
30
0.9956473
20
0.9982041
10
0.9996996
4
0.9999720
0
0.9998395
−10
0.998117
−20
0.993547
−30
0.983854
The values below 0 °C refer to supercooled water.

[edit] Density of saltwater and ice
The density of water is dependent on the temperature of the water. This is because the density is different for salt water than for fresh water. Ice still floats in the oceans, otherwise they would freeze from the bottom up. However, the salt content of oceans lowers the freezing point by about 2 °C and lowers the temperature of the density maximum of water to the freezing point. That is why, in ocean water, the downward convection of colder water is not blocked by an expansion of water as it becomes colder near the freezing point. The oceans' cold water near the freezing point continues to sink. For this reason, any creature attempting to survive at the bottom of such cold water as the Arctic Ocean generally lives in water that is 4 °C colder than the temperature at the bottom of frozen-over fresh water lakes and rivers in winter.
As the surface of salt water begins to freeze (at −1.9 °C for normal salinity seawater, 3.5%) the ice that forms is essentially salt free with a density approximately equal to that of freshwater ice. This ice floats on the surface and the salt that is "frozen out" adds to the salinity and density of the seawater just below it, in a process known as brine rejection. This more dense saltwater sinks by convection and the replacing seawater is subject to the same process. This provides essentially freshwater ice at −1.9 °C on the surface. The increased density of the seawater beneath the forming ice causes it to sink towards the bottom.

[edit] Compressibility
The compressibility of water is a function of pressure and temperature. At 0 °C in the limit of zero pressure the compressibility is 5.1×107 bar−1.[5] In the zero pressure limit the compressibility reaches a minimum of 4.4×107 bar−1 around 45 °C before increasing again with increasing temperature. As the pressure is increased the compressibility decreases, being 3.9×107 bar−1 at 0 °C and 1000 bar. The bulk modulus of water is 2.2×109 Pa.[6] The low compressibility of non-gases, and of water in particular, leads to them often being incorrectly labelled as incompressible. The low compressibility of water means that even in the deep oceans at 4000 m depth, where pressures are 4×107 Pa, there is only a 1.8% decrease in volume.[7]

[edit] Triple point
The temperature and pressure at which solid, liquid, and gaseous water coexist in equilibrium is called the triple point of water. This point is used to define the units of temperature (the kelvin and, indirectly, the degree Celsius and even the degree Fahrenheit). The triple point is at a temperature of 273.16 K (0.01 °C) by convention, and at a pressure of 611.73 Pa. This pressure is quite low, about 1/166 of the normal sea level barometric pressure of 101,325 Pa. The atmospheric surface pressure on planet Mars is remarkably close to the triple point pressure, and the zero-elevation or "sea level" of Mars is defined by the height at which the atmospheric pressure corresponds to the triple point of water.

[edit] Mpemba effect
The Mpemba effect is the surprising phenomenon whereby hot water can, under certain conditions, freeze sooner than cold water, even though it must pass the lower temperature on the way to freezing. However, this can be explained with evaporation, convection, supercooling, and the insulating effect of frost.

[edit] Hot ice
Hot ice is the name given to another surprising phenomenon in which water at room temperature can be turned into ice that remains at room temperature by supplying an electric field on the order of 106 volts per meter.[8]
The effect of such electric fields has been suggested as an explanation of cloud formation. The first time cloud ice forms around a clay particle, it requires a temperature of −10 °C, but subsequent freezing around the same clay particle requires a temperature of just −5 °C, suggesting some kind of structural change.[9]

[edit] Surface tension
Water drops are stable, due to the high surface tension of water, 72.8 mN/m, the highest of the non-metallic liquids. This can be seen when small quantities of water are put on a surface such as glass: the water stays together as drops. This property is important for life. For example, when water is carried through xylem up stems in plants the strong intermolecular attractions hold the water column together. Strong cohesive properties hold the water column together, and strong adhesive properties stick the water to the xylem, and prevent tension rupture caused by transpiration pull. Other liquids with lower surface tension would have a higher tendency to "rip", forming vacuum or air pockets and rendering the xylem water transport inoperative.

[edit] Electrical properties
Pure water containing no ions is an excellent insulator, however, not even "deionized" water, is completely free of ions. Water undergoes auto-ionisation at any temperature above absolute zero. Further, because water is such a good solvent, it almost always has some solute dissolved in it, most frequently a salt. If water has even a tiny amount of such an impurity, then it can conduct electricity readily, as impurities such as salt separate into free ions in aqueous solution by which an electric current can flow.
Water can be split into its constituent elements, hydrogen and oxygen, by passing a current through it. This process is called electrolysis. Water molecules naturally dissociate into H+ and OH− ions, which are pulled toward the cathode and anode, respectively. At the cathode, two H+ ions pick up electrons and form H2 gas. At the anode, four OH− ions combine and release O2 gas, molecular water, and four electrons. The gases produced bubble to the surface, where they can be collected. It is known that the theoretical maximum electrical resistivity for water is approximately 182 kilohm-m2/m (or 18.2 MΩ·cm2/cm) at 25 °C. This figure agrees well with what is typically seen on reverse osmosis, ultrafiltered and deionized ultrapure water systems used for instance, in semiconductor manufacturing plants. A salt or acid contaminant level exceeding that of even 100 parts per trillion (ppt) in ultrapure water will begin to noticeably lower its resistivity level by up to several kilohm-square meters/meter (a change of several hundred nanosiemens per meter of conductance).

[edit] Dipolar nature of water
An important feature of water is its polar nature. The water molecule forms an angle, with hydrogen atoms at the tips and oxygen at the vertex. Since oxygen has a higher electronegativity than hydrogen, the side of the molecule with the oxygen atom has a partial negative charge. A molecule with such a charge difference is called a dipole. The charge differences cause water molecules to be attracted to each other (the relatively positive areas being attracted to the relatively negative areas) and to other polar molecules. This attraction is known as hydrogen bonding, and explains many of the properties of water. Certain molecules, such as carbon dioxide, also have a difference in electronegativity between the atoms but the difference is that the shape of carbon dioxide is symmetrically aligned and so the opposing charges cancel one another out. This phenomenon of water can be seen if you hold an electrical source near a thin stream of water falling vertically, causing the stream to bend towards the electrical source.
Although hydrogen bonding is a relatively weak attraction compared to the covalent bonds within the water molecule itself, it is responsible for a number of water's physical properties. One such property is its relatively high melting and boiling point temperatures; more heat energy is required to break the hydrogen bonds between molecules. The similar compound hydrogen sulfide (H2S), which has much weaker hydrogen bonding, is a gas at room temperature even though it has twice the molecular mass of water. The extra bonding between water molecules also gives liquid water a large specific heat capacity. This high heat capacity makes water a good heat storage medium.
Hydrogen bonding also gives water its unusual behavior when freezing. When cooled to near freezing point, the presence of hydrogen bonds means that the molecules, as they rearrange to minimize their energy, form the hexagonal crystal structure of ice that is actually of lower density: hence the solid form, ice, will float in water. In other words, water expands as it freezes, whereas almost all other materials shrink on solidification.
An interesting consequence of the solid having a lower density than the liquid is that ice will melt if sufficient pressure is applied. With increasing pressure the melting point temperature drops and when the melting point temperature is lower than the ambient temperature the ice begins to melt. A significant increase of pressure is required to lower the melting point temperature by very much—the pressure exerted by an ice skater on the ice would only reduce the melting point by approximately 0.09 °C.

[edit] Water as a solvent
Water is also a good solvent due to its polarity. When an ionic or polar compound enters water, it is surrounded by water molecules (Hydration). The relatively small size of water molecules typically allows many water molecules to surround one molecule of solute. The partially negative dipole ends of the water are attracted to positively charged components of the solute, and vice versa for the positive dipole ends.
In general, ionic and polar substances such as acids, alcohols, and salts are relatively soluble in water, and nonpolar substances such as fats and oils are not. Nonpolar molecules stay together in water because it is energetically more favorable for the water molecules to hydrogen bond to each other than to engage in van der Waals interactions with nonpolar molecules.
An example of an ionic solute is table salt; the sodium chloride, NaCl, separates into Na+ cations and Cl- anions, each being surrounded by water molecules. The ions are then easily transported away from their crystalline lattice into solution. An example of a nonionic solute is table sugar. The water dipoles make hydrogen bonds with the polar regions of the sugar molecule (OH groups) and allow it to be carried away into solution.

[edit] Amphoteric nature of water
Chemically, water is amphoteric — i.e., it is able to act as either an acid or a base. Occasionally the term hydroxic acid is used when water acts as an acid in a chemical reaction. At a pH of 7 (neutral), the concentration of hydroxide ions (OH−) is equal to that of the hydronium (H3O+) or hydrogen (H+) ions. If the equilibrium is disturbed, the solution becomes acidic (higher concentration of hydronium ions) or basic (higher concentration of hydroxide ions).
Water can act as either an acid or a base in reactions. According to the Brønsted-Lowry system, an acid is defined as a species which donates a proton (an H+ ion) in a reaction, and a base as one which receives a proton. When reacting with a stronger acid, water acts as a base; when reacting with a stronger base, it acts as an acid. For instance, it receives an H+ ion from HCl in the equilibrium:
HCl + H2O ⇌ H3O+ + Cl−
Here water is acting as a base, by receiving an H+ ion.
In the reaction with ammonia, NH3, water donates an H+ ion, and is thus acting as an acid:
NH3 + H2O ⇌ NH4+ + OH−

[edit] Acidity in nature
In theory, pure water has a pH of 7 at 298 K. In practice, pure water is very difficult to produce. Water left exposed to air for any length of time will rapidly dissolve carbon dioxide, forming a dilute solution of carbonic acid, with a limiting pH of about 5.7. As cloud droplets form in the atmosphere and as raindrops fall through the air minor amounts of CO2 are absorbed and thus most rain is slightly acidic. If high amounts of nitrogen and sulfur oxides are present in the air, they too will dissolve into the cloud and rain drops producing more serious acid rain problems.

[edit] Hydrogen bonding in water
A water molecule can form a maximum of four hydrogen bonds because it can accept two and donate two hydrogens. Other molecules like hydrogen fluoride, ammonia, methanol form hydrogen bonds but they do not show anomalous behaviour of thermodynamic, kinetic or structural properties like those observed in water. The answer to the apparent difference between water and other hydrogen bonding liquids lies in the fact that apart from water none of the hydrogen bonding molecules can form four hydrogen bonds either due to an inability to donate/accept hydrogens or due to steric effects in bulky residues. In water local tetrahedral order due to the four hydrogen bonds gives rise to an open structure and a 3-dimensional bonding network, which exists in contrast to the closely packed structures of simple liquids. There is a great similarity between water and silica in their anomalous behaviour, even though one (water) is a liquid which has a hydrogen bonding network while the other (silica) has a covalent network with a very high melting point. One reason that water is well suited, and chosen, by life-forms, is that it exhibits its unique properties over a temperature regime that suits diverse biological processes, including hydration.
It is believed that hydrogen bond in water is largely due to electrostatic forces and some amount of covalency. The partial covalent nature of hydrogen bond predicted by Linus Pauling in 1930s is yet to be proven unambiguously by experiments and theoretical calculations.

[edit] Quantum properties of molecular water
Although the molecular formula of water is generally considered to be a stable result in molecular thermodynamics, recent work, started in 1995 has shown that at certain scales, water may act more like H3/2O than H2O at the subatomic quantum level.[10] This result could have significant ramifications at the level of, for example, the hydrogen bond in biological, chemical and physical systems. The experiment shows that when neutrons and protons collide with water, they scatter in a way that indicates that they only are affected by a ratio of 1.5:1 of hydrogen to oxygen respectively. However, the time-scale of this response is only seen at the level of attoseconds (10-18 seconds), and so is only relevant in highly resolved kinetic and dynamical systems.[11][12]

[edit] History
The properties of water have historically been used to define various temperature scales. Notably, the Kelvin, Celsius and Fahrenheit scales were, or currently are, defined by the freezing and boiling points of water. The less common scales of Delisle, Newton, Réaumur and Rømer were defined similarly. The triple point of water is a more commonly used standard point today.[13]
The first scientific decomposition of water into hydrogen and oxygen, by electrolysis, was done in 1800 by William Nicholson, an English chemist. In 1805, Joseph Louis Gay-Lussac and Alexander von Humboldt showed that water is composed of two parts hydrogen and one part oxygen (by volume).
Gilbert Newton Lewis isolated the first sample of pure heavy water in 1933.
Polywater was a hypothetical polymerized form of water that was the subject of much scientific controversy during the late 1960s. The consensus now is that it does not exist.

[edit] Systematic naming
The accepted IUPAC name of water is simply "water", although there are two other systematic names which can be used to describe the molecule.
The simplest and best systematic name of water is hydrogen oxide. This is analogous to related compounds such as hydrogen peroxide, hydrogen sulfide, and deuterium oxide (heavy water). Another systematic name, oxidane, is accepted by IUPAC as a parent name for the systematic naming of oxygen-based substituent groups,[14] although even these commonly have other recommended names. For example, the name hydroxyl is recommended over oxidanyl for the –OH group. The name oxane is explicitly mentioned by the IUPAC as being unsuitable for this purpose, since it is already the name of a cyclic ether also known as tetrahydropyran in the Hantzsch-Widman system; similar compounds include dioxane and trioxane.

[edit] Systematic nomenclature and humor
Main article: dihydrogen monoxide hoax
Chemists sometimes refer to water as dihydrogen monoxide or DHMO, an overly pedantic systematic covalent name of this molecule, especially in parodies of chemical research that call for this "lethal chemical" to be banned. In reality, a more realistic systematic name would be hydrogen oxide, since the "di-" and "mon-" prefixes are superfluous. Hydrogen sulfide, H2S, is never referred to as "dihydrogen monosulfide", and hydrogen peroxide, H2O2, is never called "dihydrogen dioxide".
Some overzealous material safety data sheets for water list the following: Caution: May cause drowning!
The systematic acid name of water is hydroxic acid or hydroxilic acid. Likewise, the systematic alkali name of water is hydrogen hydroxide—both acid and alkali names exist for water because it is able to react both as an acid or an alkali, depending on the strength of the acid or alkali it is reacted with (amphoteric). None of these names are used widely outside of DHMO sites.