Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at temperatures above 0 °C (273.15 K, 32 °F) at sea level, but it often co-exists on Earth with its solid state, ice, and gaseous state (water vapor or steam). Water also exists in a liquid crystal state near hydrophilic surfaces.

Water covers 71% of the Earth's surface, and is vital for all known forms of life. On Earth, 96.5% of the planet's water is found in oceans, 1.7% in groundwater, 1.7% in glaciers and the ice caps of Antarctica and Greenland, a small fraction in other large water bodies, and 0.001% in the air as vapor, clouds (formed of solid and liquid water particles suspended in air), and precipitation. Only 2.5% of the Earth's water is freshwater, and 98.8% of that water is in ice and groundwater. Less than 0.3% of all freshwater is in rivers, lakes, and the atmosphere, and an even smaller amount of the Earth's freshwater (0.003%) is contained within biological bodies and manufactured products.

Water on Earth moves continually through the hydrological cycle of evaporation and transpiration (evapotranspiration), condensation, precipitation, and runoff, usually reaching the sea. Evaporation and transpiration contribute to the precipitation over land.

Safe drinking water is essential to humans and other lifeforms. Access to safe drinking water has improved over the last decades in almost every part of the world, but approximately one billion people still lack access to safe water and over 2.5 billion lack access to adequate sanitation. There is a clear correlation between access to safe water and GDP per capita. However, some observers have estimated that by 2025 more than half of the world population will be facing water-based vulnerability. A recent report (November 2009) suggests that by 2030, in some developing regions of the world, water demand will exceed supply by 50%. Water plays an important role in the world economy, as it functions as a solvent for a wide variety of chemical substances and facilitates industrial cooling and transportation. Approximately 70% of the fresh water used by humans goes to agriculture.

Read more about WaterChemical and Physical Properties, Taste and Odor, On Earth, Effects On Life, Effects On Human Civilization, Water Law, Water Politics and Water Crisis

Other articles related to "water":

Litre - Definition
... From 1901 to 1964, the litre was defined as the volume of one kilogram of pure water at 4 °C and 760 millimetres of mercury pressure ... in France and was intended to be of the same mass as the 1 litre of water referred to above ... Additionally, the mass-volume relationship of water (as with any fluid) depends on temperature, pressure, purity, and isotopic uniformity ...
Water - In Culture - Literature
... Water is used in literature as a symbol of purification ... Sherlock Holmes held that "From a drop of water, a logician could infer the possibility of an Atlantic or a Niagara without having seen or heard of one or the other." ...
Synchronized Swimming - History
... At the turn of the 20th century, synchronized swimming was known as water ballet ... Glasgow which were equipped with huge on-stage water tanks for the purpose ... After experimenting with various diving actions and stunts in the water, Katherine Curtis started one of the first water ballet clubs at the University of Chicago, where the team began ...
... consisting of fine granular material (such as sand or silt), clay, and water ... When water in the sand cannot escape, it creates liquefied soil that loses strength and cannot support weight ... Quicksand can be formed in standing water or in upwards flowing water (as from an artesian spring) ...
Natural Gas - Safety Concerns - Production
... Subsidence may affect ecosystems, waterways, sewer and water supply systems, foundations, and so on ... force 1 to 9 million US gallons (34,000 m3) of water mixed with a variety of chemicals through the wellbore casing into the shale ... The high pressure water breaks up or "fracks" the shale, which releases the trapped gas ...

Famous quotes containing the word water:

    Communism, my friend, is more than Marxism, just as Catholicism ... is more than the Roman Curia. There is a mystique as well as a politique.... Catholics and Communists have committed great crimes, but at least they have not stood aside, like an established society, and been indifferent. I would rather have blood on my hands than water like Pilate.
    Graham Greene (1904–1991)

    The point of the dragonfly’s terrible lip, the giant water bug, birdsong, or the beautiful dazzle and flash of sunlighted minnows, is not that it all fits together like clockwork--for it doesn’t ... but that it all flows so freely wild, like the creek, that it all surges in such a free, finged tangle. Freedom is the world’s water and weather, the world’s nourishment freely given, its soil and sap: and the creator loves pizzazz.
    Annie Dillard (b. 1945)

    We have to learn how to come out of unclean situations cleaner than we were, and even how to wash ourselves with dirty water when we need to.
    Friedrich Nietzsche (1844–1900)