Water
Water (chemical formula
H2O) is an
inorganic, transparent, tasteless, odorless, and
nearly colorless chemical substance, which is the main constituent of
Earth's
hydrosphere and the
fluids of all known living organisms (in which it acts as a
solvent[1]). It is vital for all known forms of
life, despite providing neither
food, energy, nor organic
micronutrients. Its
chemical formula, H2O, indicates that each of its
molecules contains one
oxygen and two
hydrogen atoms, connected by
covalent bonds. The hydrogen atoms are attached to the oxygen atom at an angle of 104.45°.
[2] "Water" is also the name of the liquid state of H2O at
standard temperature and pressure.
A number of natural states of water exist. 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% of the Earth's surface, with seas and oceans making up most of the water volume on earth (about 96.5%).
[3] 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%).
[4][5] 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 freshwater used by
humans goes to agriculture.
[6] 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.
[7] 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 and skiing.
