Water is a transparent, tasteless, odorless, and nearly colorless chemical substance that is the main constituent of
Earth 's streams, lakes , and oceans , and the fluids of most living organisms. Its chemical formula is H2O, meaning that each of its molecules contains
one oxygen and two hydrogen
atoms that are connected by covalent bonds. Strictly speaking, water refers to the liquid state of a substance that prevails at standard
ambient temperature and pressure; but it often refers also to its solid state (ice) or its
gaseous state ( steam or water vapor ). It also occurs in nature as snow , glaciers, ice packs and icebergs,
clouds , fog , dew , aquifers, and atmospheric humidity.
Water covers 71% of the
Earth 's surface. It is vital for all known forms of life . On
Earth , 96.5% of the planet 's
crust water is found in seas and 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, 0.001% in the air as vapor,
clouds (formed of ice and liquid water suspended in air ), and precipitation . Only 2.5% of this water is freshwater, and 98.8% of that water is in ice (excepting ice in
clouds ) 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. A greater quantity of water is found in the
earth 's interior.
