Water

Warning: mkdir() [function.mkdir]: Permission denied in /home/webs/affiliatelib2/CacheManager.php on line 12

Warning: mkdir() [function.mkdir]: No such file or directory in /home/webs/affiliatelib2/CacheManager.php on line 12

Warning: fopen(/home/templatecore2cache//*cluesnet.com/ac/ac717c52ce211933ddc44ba42e41c4057a83c4e6.tc2cache) [function.fopen]: failed to open stream: No such file or directory in /home/webs/affiliatelib2/CacheManager.php on line 130

Warning: fwrite(): supplied argument is not a valid stream resource in /home/webs/affiliatelib2/CacheManager.php on line 131

Warning: fclose(): supplied argument is not a valid stream resource in /home/webs/affiliatelib2/CacheManager.php on line 132

s.Water is a common chemical substance that is essential to all known forms of life.http://pubs.acs.org/cgi-bin/abstract.cgi/bichaw/1997/36/i43/abs/bi971323j.htmlIn typical usage, water refers only to its liquid form or States of matter, but the substance also has a solid state, ice, and a gaseous state, water vapor. About 1,460 Tonne#Multiples (Tt) 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 aquifers and 0.001% in the atmosphere as vapor, clouds (formed of solid and liquid water particles suspended in air), and precipitation (meteorology). Water Vapor in the Climate System, Special Report, , December 1995 (linked 4/2007). Vital Water UNEP. Some of the Earth's water is contained within man-made and natural objects near the Earth's surface such as water towers, animal and plant bodies, manufactured products, and food stores.

Seawater oceans hold 97% of surface water, glaciers and polar ice caps 2.4%, and other land surface water such as rivers and lakes 0.6%. Water moves continually through a water cycle of evaporation or transpiration, precipitation (meteorology), and runoff (water), 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. In many parts of the world, it is in short supply. Many organic molecules as well as salts, sugars, acids, alkalis, and some gases (especially oxygen), are solvent in water.

Beyond the Earth, a significant quantity of water is thought to exist underground on the planet Mars, on the moons Europa (moon) and Enceladus (moon), and on the exoplanets known as HD 189733 b Water Found on Distant Planet July 12, 2007 By LAURA BLUE TIME and HD 209458 b. Water Found in Extrasolar Planet's Atmosphere - Space.com

's surface; the oceans 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 clouds, contributing to the Earth's albedo.

Chemical and physical properties {| align="right" border="1" cellspacing="0" cellpadding="3" style="margin: 0 0 0 0.5em; background: #FFFFFF; border-collapse: collapse; border-color: #C0C090;"! | Water (molecule)|-| align="center" colspan="2" bgcolor="#ffffff" | Water is the base of all life, and
an abundant chemical compound on the earth's surface.|-! | Information and properties|-| IUPAC nomenclature| water|-| Alternative names| aqua, dihydrogen monoxide,
hydrogen hydroxide, (wikt:wikisaurus:water)|-| Molecular formula| InChI=1/H2O/h1H2|-| [Molar mass and [Phase (matter)| 0.998 g/cm³ (liquid at 20 °C)
0.92 g/cm³ (solid)|-| Melting point (273.15 [kelvin) (32 Fahrenheit)|-| Boiling point| 4.184 J/(g·K) (liquid at 20 °C)|-! | [Water (data page)|-| align="center" cellspacing="3" style="border: 1px solid #C0C090; background-color: #F8EABA; margin-bottom: 3px;" colspan="2" |wikipedia:Chemical infobox|-|}

Water is the chemical substance with chemical formula hydrogen2oxygen: one molecule of water has two hydrogen atoms covalently chemical bond to a single oxygen atom. Water is a tasteless, odorless liquid at standard conditions, and appears colorless in small quantities, although it has its own intrinsic very light blue hue. Ice also appears colorless, and water vapor is essentially invisible as a gas.Water is primarily a liquid under standard conditions, which is not predicted from its relationship to other analogous hydrides of the Chalcogen in the periodic table, which are gases such as hydrogen sulfide. Also the elements surrounding oxygen in the periodic table, nitrogen, fluorine, phosphorus, sulfur and chlorine, all combine with hydrogen to produce gases under standard conditions. The reason that oxygen hydride (water) forms a liquid is that it is more electronegative than all of these elements (other than fluorine). Oxygen attracts electrons much more strongly than hydrogen, resulting in a net positive charge on the hydrogen atoms, and a net negative charge on the oxygen atom. The presence of a charge on each of these atoms gives each water molecule a net dipole moment. Electrical attraction between water molecules due to this dipole pulls individual molecules closer together, making it more difficult to separate the molecules and therefore raising the boiling point. This attraction is known as hydrogen bonding. Water can be described as a polar liquid that dissociates disproportionately into the hydronium ion (H3O+(aq)) and an associated hydroxide ion (OH−(aq)).Water is in dynamic equilibrium between the liquid, gas and solid states of matter at standard temperature and pressure, and is the only pure substance found naturally on Earth to be so.

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

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

Surface tension is under the water level, which has risen gently and smoothly. Surface tension prevents the water from submerging the flower.

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

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

Solvation make the water of Havasu Falls appear turquoise.Water is a very strong solvent, referred to as the universal solvent, dissolving many types of substances. Substances that will mix well and dissolve in water (e.g. salts) are known as "hydrophilic" (water-loving) substances, while those that do not mix well with water (e.g. lipids), are known as "hydrophobic" (water-fearing) substances. The ability of a substance to dissolve in water is determined by whether or not the substance can match or better the strong intermolecular force#Dipole-dipole interactions that water molecules generate between other water molecules. If a substance has properties that do not allow it to overcome these strong intermolecular forces, the molecules are "precipitation (chemistry)" from the water, and do not dissolve. Contrary to the common misconception, water and hydrophobic substances does not "repel", and the hydration of a hydrophobic surface is energetically, but not entropically, favorable.

Electrical conductivity Pure water has a low electrical conductivity, but this increases significantly upon solvation of a small amount of ionic material water such as hydrogen chloride. Thus the risks of electric shock are much greater in water with the usual impurities not found in pure water. Any electrical properties observable in water are from the ions of mineral salts and carbon dioxide dissolved in it. self-ionization of water where two water molecules become one hydroxide anion and one hydronium cation, but not enough to carry enough electric current to do any work or harm for most operations. In pure water, sensitive equipment can detect a very slight electrical electrical conductivity of 0.055 Siemens (unit)/Centimeter at 25 °C. Water can also be electrolysis into oxygen and hydrogen gases but in the absence of dissolved ions this is a very slow process, as very little current is conducted. While electrons are the primary charge carriers in water (and metals), in ice (and some other electrolytes), protons are the primary carriers (see proton conductor).

Heavy Water and isotopologues of water Hydrogen has three isotopes. The most common, making up more than 95% of water, has 1 proton and 0 neutrons. A second isotope, deuterium (short form "D"), has 1 proton and 1 neutron. Deuterium, , is also known as heavy water and is used in nuclear reactors as a neutron moderator. The third isotope, tritium, has 1 proton and 2 neutrons, and is radioactive, with a half-life of 12.32 years. exists in nature only in tiny quantities, being produced primarily via cosmic ray-driven nuclear reactions in the atmosphere. is stable, but differs from in in that it is more dense - hence, "heavy water" - and in that several other physical properties are slightly different from those of common, Hydrogen-1 containing "light water". occurs naturally in ordinary water in very low concentrations. Consumption of pure isolated may affect biochemical processes - ingestion of large amounts impairs kidney and central nervous system function. However, very large amounts of heavy water must be consumed for any toxicity to be apparent, and smaller quantities can be consumed with no ill effects at all.

Water, ice, and vapor Heat capacity and heat of vaporization Water has the second highest specific heat capacity of any known chemical compound, after ammonia, as well as a high heat of vaporization (40.65 kJ mol−1), both of which are a result of the extensive hydrogen bonding between its molecules. These two unusual properties allow water to moderate Earth's climate by buffering large fluctuations in temperature.

Freezing point A simple but environmentally important and unusual property of water is that its usual solid form, ice, floats on its liquid form. This solid state is not as dense as liquid water because of the geometry of the hydrogen bonds which are formed only at lower temperatures. For almost all other substances the solid form has a greater density than the liquid form. Fresh water at standard atmospheric pressure is most dense at 3.98 °C, and will sink by convection as it cools to that temperature, and if it becomes colder it will rise instead. This reversal will cause deep water to remain warmer than shallower freezing water, so that ice in a body of water will form first at the surface and progress downward, while the majority of the water underneath will hold a constant 4 °C. This effectively insulates a lake floor from the cold.The water will freeze at 0 °C (32 °F, 273 K), however, it can be supercooled in a fluid state down to its nucleation at almost 231 K (−42 °C)P. G. Debenedetti, P. G., and Stanley, H. E.; "Supercooled and Glassy Water", Physics Today 56 (6), p. 40–46 (2003)..Ice also has a number of more exotic phases not commonly seen (go to the full article on Ice).

Triple point {| class="wikitable" style="float:right;"|+The various triple points of water!Phases in stable equilibrium!Pressure!Temperature|-|liquid water, ice I, and water vapour], and ice III|350.1 MPa| -17.0 °C|-|liquid water, ice V, and [ice VI, and ice III|213 MPa| -35 °C|-|ice II, ice III, and ice V|344 MPa| -24 °C|-|ice II, ice V, and ice VI|626 MPa| -70 °C|}The [triple point of water (the single combination of pressure and temperature at which pure liquid water, ice, and water vapor can coexist in a stable equilibrium) is used to define the kelvin, the SI unit of thermodynamic temperature. As a consequence, water's triple point temperature is a prescribed value rather than a measured quantity: 273.16 kelvins (0.01 °C) and a pressure of 611.73 pascals (approximately 0.0060373 atmosphere (unit)).This is approximately the combination that exists with 100% relative humidity at sea level and the freezing point of water.

Although it is commonly named as "the triple point of water", the stable combination of liquid water, ice I, and water vapour is but one of several triple points on the phase diagram of water. Gustav Heinrich Johann Apollon Tammann in Göttingen produced data on several other triple points in the early 20th century. Kamb and others documented further triple points in the 1960s.

Miscibility and condensation Water is miscible with many liquids, for example ethanol in all proportions, forming a single homogeneous liquid. On the other hand water and most oils are immiscible usually forming layers according to increasing density from the top.

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

Water on Earth Origin and planetary effects along center row range of possible habitable zones of varying size stars.Much of the universe's water may be produced as a byproduct of star formation.When stars are born, their birth is accompanied by a strong outward wind of gas and dust. When this outflow of material eventually impacts the surrounding gas, the shock waves that are created compress and heat the gas. The water observed is quickly produced in this warm dense gas.Gary Melnick, Harvard-Smithsonian Center for Astrophysics and David Neufeld, Johns Hopkins University quoted in:.(linked 4/2007) Solar distance and Earth gravity The existence of liquid water, and to a lesser extent its gaseous and solid forms, on Earth is vital to the existence of life on Earth. The Earth is located in the habitable zone of the solar system; if it were slightly closer to or further from the Sun (about 5%, or 8 million kilometers or so), the conditions which allow the three forms to be present simultaneously would be far less likely to exist.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 The Encyclopedia of Astrobiology, Astronomy and Spaceflight.

Earth's mass allows gravity to hold an Celestial body 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 caps (as on Mars (planet)).

It has been proposed that life itself may maintain the conditions that have allowed its continued existence. The surface temperature of Earth has been relatively constant through geologic time despite varying levels of incoming solar radiation (insolation), indicating that a dynamic process governs Earth's temperature via a combination of greenhouse gases and surface or atmospheric albedo. This proposal is known as the Gaia hypothesis.

The state of water also depends on a planet's gravity. If a planet is sufficiently massive, the water on it may be solid even at high temperatures, because of the high pressure caused by gravity.

Tides {{imageframe|width=240|content=|caption=High tide (left) and low tide (right).-->Tides are the cyclic rising and falling of Earth's ocean surface caused by the tidal forces of the Moon and the Sun acting on the oceans. Tides cause changes in the depth of the marine and estuary water bodies and produce oscillating currents known as tidal streams.The changing tide produced at a given location is the result of the changing positions of the Moon and Sun relative to the Earth coupled with the Coriolis effect and the local bathymetry.The strip of seashore that is submerged at high tide and exposed at low tide, the intertidal zone, is an important ecological product of ocean tides.

Water cycle The biosphere can be roughly divided into oceans, land, and atmosphere.Water moves perpetually through each of these regions in the water cycle consisting of following transfer processes:

evaporation from oceans and other water bodies into the air and transpiration from land plants and animals into air.
precipitation (meteorology), from water vapor condensing from the air and falling to earth or ocean.
runoff (water) from the land usually reaching the sea.

Most water vapor over the oceans returns to the oceans, but winds carry water vapor over land at the same rate as runoff into the sea, about 36 Tonne#Multiples 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 rainbows.

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

Fresh water storage Some runoff water is trapped for periods, for example in lakes.At high altitude, during winter, and in the far north and south, snow collects in ice caps, snow pack and glaciers.Water also infiltrates the ground and goes into aquifers. This groundwater later flows back to the surface in spring (hydrosphere), or more spectacularly in hot springs and geysers. Groundwater is also extracted artificially in water wells.This water storage is important, since clean, fresh water is essential to human and other land-based life. In many parts of the world, it is in short supply., 1902 Forms of water Water takes many different forms on Earth: water vapor and clouds in the sky; seawater and rarely icebergs in the ocean; glaciers and rivers in the mountains; and aquifers in the ground.

Water can dissolve many different substances, giving it different tastes and odours. In fact, humans and other animals have developed senses to be able to evaluate the drinking water of water: animals generally dislike the taste of salty sea water and the putrid swamps and favor the purer water of a mountain spring or aquifer. The taste advertised in spring water or mineral water derives from the minerals dissolved in it, as pure H2O is tasteless. As such, purity in spring and mineral water refers to purity from toxins, pollutants, and microorganisms.

Effects on life of a coral reefFrom a biology 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 compounds to react in ways that ultimately allow replication. All known forms of life depend on water. Water is vital both as a solvent in which many of the body's solutes dissolve and as an essential part of many metabolism processes within the body. Metabolism is the sum total of anabolism and catabolism. In anabolism, water is removed from molecules (through energy requiring enzymatic chemical reactions) in order to grow larger molecules (e.g. starches, triglycerides and proteins for storage of fuels and information). In catabolism, water is used to break bonds in order to generate smaller molecules (e.g. glucose, fatty acids and amino acids to be used for fuels for energy use or other purposes). Water is thus essential and central to these metabolic processes. Therefore, without water, these metabolic processes would cease to exist, leaving us to muse about what processes would be in its place, such as gas absorption, dust collection, etc.

Water is also central to photosynthesis and respiration. Photosynthetic cells use the sun's energy to split off water's hydrogen from oxygen. Hydrogen is combined with CO2 (absorbed from air or water) to form glucose and release oxygen. All living cells use such fuels and oxidize the hydrogen and carbon to capture the sun's energy and reform water and CO2 in the process (cellular respiration).

Water is also central to acid-base neutrality and enzyme function. An acid, a hydrogen ion (H+, that is, a proton) donor, can be neutralized by a base, a proton acceptor such as hydroxide ion (OH−) to form water. Water is considered to be neutral, with a pH (the negative log of the hydrogen ion concentration) of 7. Acids have pH values less than 7 while bases have values greater than 7. Stomach acid (HCl) is useful to digestion. However, its corrosive effect on the esophagus during reflux can temporarily be neutralized by ingestion of a base such as aluminum hydroxide to produce the neutral molecules water and the salt aluminum chloride. Human biochemistry that involves enzymes usually performs optimally around a biologically neutral pH of 7.4.

Aquatic life forms s - a key phytoplankton groupEarth's waters are filled with life. Nearly all fish live exclusively in water, and there are many types of marine mammals, such as dolphins and whales that also live in the water. Some kinds of animals, such as amphibians, spend portions of their lives in water and portions on land. Plants such as kelp and algae grow in the water and are the basis for some underwater ecosystems. Plankton is generally the foundation of the ocean food chain.

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

Effects on human civilization Civilization has historically flourished around rivers and major waterways; Mesopotamia, the so-called cradle of civilization, was situated between the major rivers Tigris and Euphrates; the ancient society of the Egyptians depended entirely upon the Nile. Large metropolises like Rotterdam, London, Montreal, Paris, New York City, Shanghai, Tokyo, Chicago, and Hong Kong owe their success in part to their easy accessibility via water and the resultant expansion of trade. Islands with safe water ports, like Singapore, have flourished for the same reason. In places such as North Africa and the Middle East, where water is more scarce, access to clean drinking water was and is a major factor in human development.

Health and pollution Water fit for human consumption is called drinking water or potable water. Water that is not potable can be made potable by distillation (heating it until it becomes water vapor, and then capturing the vapor without any of the impurities it leaves behind), or by other methods (chemical or heat treatment that kills bacteria). Sometimes the term safe water is applied to potable water of a lower quality threshold (i.e., it is used effectively for nutrition in humans that have weak access to water cleaning processes, and does more good than harm). Water that is not fit for drinking but is not harmful for humans when used for swimming or bathing is called by various names other than potable or drinking water, and is sometimes called safe water, or "safe for bathing". Chlorine is a skin and mucous membrane irritant that is used to make water safe for bathing or drinking. Its use is highly technical and is usually monitored by government regulations (typically 1 part per million (ppm) for drinking water, and 1-2 ppm of chlorine not yet reacted with impurities for bathing water).

This natural resource is becoming scarcer in certain places, and its availability is a major social and economic concern. Currently, about 1 billion people around the world routinely drink unhealthy water. Most countries accepted the goal of halving by 2015 the number of people worldwide who do not have access to safe water and sanitation during the 29th G8 summit. G8 "Action plan" decided upon at the 2003 Evian summit Even if this difficult goal is met, it will still leave more than an estimated half a billion people without access to safe drinking water and over 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 (like petroleum is), but rather re-circulated as potable water in precipitation in quantities many degrees of magnitude higher than human consumption. Therefore, it is the relatively small quantity of water in reserve in the earth (about 1% of our drinking water supply, which is replenished in aquifers around every 1 to 10 years), that is a non-renewable resource, and it is, rather, the distribution of potable and irrigation water which is scarce, rather than the actual amount of it that exists on the earth. Water-poor countries use importation of goods as the primary method of importing water (to leave enough for local human consumption), since the manufacturing process uses around 10 to 100 times products' masses in water.

In the developing world, 90% of all wastewater still goes untreated into local rivers and streams. Some 50 countries, with roughly a third of the world’s population, also suffer from medium or high water stress, and 17 of these extract more water annually than is recharged through their natural water cycles . The strain not only affects surface freshwater bodies like rivers and lakes, but it also degrades groundwater resources.

Human uses Agriculture In many developing nations, irrigation accounts for over 90% of water withdrawn from available sources for use. In Englandwhere rain is abundant year round, water used for agriculture accounts for less than 1% of human usage. Yet even on the same continent, water used for irrigation in Spain, Portugal and Greece exceeds 70% of total usage.Irrigation has been a key component of the green revolution that has enabled many developing countries to produce enough food to feed everyone. More water will be needed to produce more food for 3 billion more people. But increasing competition for water and inefficient irrigation practices could constrain future food production.Globally, roughly 15-35% of irrigation withdrawals are estimated to be unsustainable. The map indicates where there is insufficient freshwater to fully satisfy irrigated crop demands. WBCSD Water Faacts & Trends

As a scientific standard On 7 April 1795, the gram was defined in France to be equal to "the absolute weight of a volume of pure water equal to a cube of one hundredth of a meter, and to the temperature of the melting ice." Decree relating to the weights and measurements 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 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.Citation: L'Histoire Du Mètre, La Détermination De L'Unité De Poids, link to Web site here.

Neutral pH is defined as the natural pH of pure water.

Natural water consists mainly of the isotopes hydrogen-1 and oxygen-16, but there is a 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.

For drinking in ChinaAbout 70% of the fat free mass of the human body is made of water. To function properly, the body requires between one and seven liters of water per day to avoid dehydration; the precise amount depends on the level of activity, temperature, humidity, and other factors. Most of this is ingested through foods or beverages other than drinking straight water. It is not clear how much water intake is needed by healthy people, though most experts agree that 8–10 glasses of water (approximately 2 liters) daily is the minimum to maintain proper hydration. 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, 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. "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 There are other myths such as the effect of water on weight loss and constipation that have been dispelled. Drinking Water - How Much?, Factsmart.org web site and references within

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."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. 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. Dietary Reference Intakes: Water, Potassium, Sodium, Chloride, and Sulfate, Food and Nutrition Board Specifically, Pregnancy 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.http://www.mayoclinic.com/health/water/NU00283 Also noted is that normally, about 20 percent of water intake comes from food, while the rest comes from drinking water and beverages (Caffeine included). Water is excreted from the body in multiple forms; through urine and feces, through sweating, and by exhalation of water vapor in the breath. With physical exertion and heat exposure, water loss will increase and daily fluid needs may increase as well.

Humans require water that does not contain too many impurities. Common impurities include metal salts and/or harmful bacterium, such as Vibrio. Some solutes are acceptable and even desirable for taste enhancement and to provide needed electrolytes.

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.

As a solvent Dissolving (or suspension (chemistry)) is used to wash everyday items such as the human body, clothes, floors, cars, food, and pets. Also, human wastes are carried by water in the sewage system. Its use as a cleaning solvent consumes most of water in industrialized countries.

An advantage of water is that biological processing of wastewater is easy and treated wastewater can be safely led into the sea or a river. However, if the contaminants are toxic and not processable biologically, wastewater has to be incinerated, which is expensive.

As a heat transfer fluid Water and steam are commonly used as heat transfer fluids in diverse heat exchanger systems, because of the 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 power station, water is the coolant, which vaporizes and drives steam turbines to generate electricity.

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.

Extinguishing fires Water has a high heat of vaporization and is relatively inert, which makes it a good fire extinguishing fluid. The evaporation of water carries heat away from the fire. However, water cannot be used to fight fires of electric equipment, because impure water is electrically conductive, or oils and organic solvents, because they float on water and the explosive boiling of water tends to spread the burning liquid.

Decomposition of water that has been realized in the Chernobyl disaster. Initially, cooling of the incandescent reactor was attempted, but the result was an explosion, when the extreme heat decomposed water into hydrogen and oxygen, which subsequently exploded.

Chemical uses Organic reactions are usually quenched 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 reactions by water has been observed. Supercritical water has recently been a topic of research. Oxygen-saturated supercritical water combusts organic pollutants efficiently.

Recreation Humans use water for many recreational purposes, as well as for exercising and for sports. Some of these include swimming, waterskiing, boating, fishing, and diving. In addition, some sports, like ice hockey and ice skating, are played on ice.Lakesides and beaches are popular places for people to go to relax and enjoy recreation. Many find the sound of flowing water to be calming, too. Some keep fish and other life in aquarium or ponds for show, fun, and companionship. Humans also use water for snow sports i.e. skiing or snowboarding, which requires the water to be frozen.People may also use water for play fighting such as with snowballs, water guns or water balloons.They may also make fountains and use water in their public or private decorations.

Industrial applications Pressurized water is used in water blasting and water jet cutters. Also, very high pressure water guns are used for precise cutting. It works very well, is relatively safe, and is not harmful to the environment.

Food processing Water plays many critical roles within the field of food science. It is important for a food scientist to understand the roles that water plays within food processing to ensure the success of their products.

Solutes such as salts and sugars found in water affect the physical properties of water. The boiling and freezing points of water is affected by solutes. One mole (unit) 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.Vaclacik and Christian, 2003 Solutes in water also affect water activity which affects many chemical reactions and the growth of microbes in food.DeMan, 1999 Water activity can be described as a ratio of the vapor pressure of water in a solution to the vapor pressure of pure water. Solutes in water lower water activity. This is important to know because most bacterial growth ceases at low levels of water activity. Not only does microbial growth affect the safety of food but also the preservation and shelf life of food.

Water hardness is also a critical factor in food processing. 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. 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. 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.

Boiling, steaming, and simmering are popular cooking methods that often require immersing food in water or its gaseous state, steam.

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.

Politics

Because of overpopulation, mass consumption, misuse, and water pollution, the availability of drinking water per capita is inadequate and shrinking as of the year 2006. For this reason, water is a strategic resource in the globe and an important element in many political conflicts. Some have predicted that clean water will become the "next oil", making Canada, with this resource in abundance, possibly the richest country in the world. There is a long history of conflict over water, including efforts to gain access to water, the use of water in wars started for other reasons, and tensions over shortages and control. A Chronology of Water-Related Conflicts 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 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. The United Nations Development Programme sums up world water distribution in the 2006 development report: "While one part of the world sustains a designer bottled-water market that generates no tangible health benefits, another part suffers acute public health risks because people have to drink water from drains or from lakes and rivers." UNDP Human Development Report 2006 United Nations Development Programme, 2006. 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 management and sustainable use.

OECD countries , Victoria, AustraliaWith nearly 2,000 cubic metres (70,000 ft3) of water per person per year , the United States leads the world in water consumption per capita. In the Organization for Economic Co-operation and Development (OECD) countries, the U.S. is first for water consumption, then Canada with 1,600 cubic meters (56,000 ft3) of water per person per year, which is about twice the amount of water used by the average person from France, three times as much as the average Germany, and almost eight times as much as the average Denmark. Since 1980, overall water use in Canada has increased by 25.7%. This is five times higher than the overall OECD increase of 4.5%. In contrast, nine OECD nations were able to decrease their overall water use since 1980 (Sweden, the Netherlands, the United States, the United Kingdom, the Czech Republic, Luxembourg,

South West Water - Home
Water and waste water services for the West Country. Details on the Clean Sweep programme, customer and corporate information.

Water UK: Working on behalf of the Water Industry for a sustainable ...
Water UK profile We actively seek to develop policy and improve understanding in areas that involve the industry, its customers and stakeholders.

Water UK: Working on behalf of the Water Industry for a sustainable ...
Working with government, regulators and stakeholder organisations to develop policy and improve understanding of the business of water on behalf of UK water and wastewater service ...

Yorkshire Water :: Home
Features consumer, corporate, environmental and leisure information including photo gallery of local beauty spots.

Welcome to the Wessex Water website
Regional water and sewage company. Offers information for customers, online bill payment facility, environmental report and also contact details.

Severn Trent Water
Severn Trent Water's website is aimed at domestic customers. It covers everything from information about our wide range of customer services, educational information, to water ...

Defra, UK - Environmental Protection - Water
We deal with all aspects of water policy in England, including water supply and resources, and the regulatory systems ...

WaterAid UK site
International NGO dedicated exclusively to the provision of safe domestic water, sanitation and hygiene education to the world's poorest people.

BBC - Health - Healthy living - Water
The facts about water ... Water. Alison Greenhalgh. Water is a vital component of our diets, it's essential for the growth and maintenance of our bodies, as it's involved in a ...

Environment Agency - Fun & Games - Water
We each consume about 150 litres of water every day. Water is essential for life and an important part of our environment. Read on to learn more about water and its uses.