Water is an
inorganic compound with the
chemical formula H2O. It is a transparent, tasteless, odorless,
[c] and
nearly colorless chemical substance. It is the main constituent of Earth's
hydrosphere and the
fluids of all known living organisms in which it acts as a
solvent. Water, being a
polar molecule, undergoes strong intermolecular
hydrogen bonding which is a large contributor to its physical and chemical properties.
[20] It is vital for all known forms of life, despite not providing
food energy or being an organic
micronutrient. Due to its presence in all organisms, its chemical stability, its worldwide abundance and its strong polarity relative to its small molecular size; water is often referred to as the "universal solvent".
[21]
Because Earth's environment is relatively close to water's
triple point, water exists on Earth as a solid, a liquid, and a gas.
[22] It forms
precipitation in the form of rain and
aerosols in the form of
fog. Clouds consist of suspended droplets of water and
ice, its solid state. When finely divided,
crystalline ice may precipitate in the form of snow. The gaseous state of water is
steam or
water vapor.
Water covers about 71.0% of the Earth's surface, with seas and oceans making up most of the water volume (about 96.5%).
[23] Small portions of water occur as
groundwater (1.7%), in the
glaciers and the
ice caps of
Antarctica and Greenland (1.7%), and in the air as
vapor, clouds (consisting of ice and liquid water suspended in air), and precipitation (0.001%).
[24][25] Water moves continually through the
water cycle of
evaporation,
transpiration (
evapotranspiration),
condensation,
precipitation, and
runoff, usually reaching the sea.
Water plays an important role in the
world economy. Approximately 70% of the
fresh water used by humans
goes to agriculture.
[26] Fishing in
salt and
fresh water bodies has been, and continues to be, a major source of food for many parts of the world, providing 6.5% of global protein.
[27] Much of the long-distance trade of commodities (such as oil, natural gas, and manufactured products) is
transported by boats through seas, rivers, lakes, and canals. Large quantities of water, ice, and steam are used for cooling and heating in industry and homes. Water is an excellent solvent for a wide variety of substances, both mineral and organic; as such, it is widely used in industrial processes and in cooking and washing. Water, ice, and snow are also central to many sports and other forms of entertainment, such as swimming, pleasure boating,
boat racing,
surfing,
sport fishing,
diving,
ice skating,
snowboarding, and
skiing.