Water is a common chemical substance that is essential for the survival of all known forms of life.In typical usage,water refers only to its liquid form or state,but the substance also has a solid state,ice,and a gaseous state,water vapor or steam.About 1.460 petatonnes (Pt) (1021kilograms) 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 air as vapor,clouds (formed of solid and liquid water particles suspended in air),and precipitation.[1] Saltwater oceans hold 97% of surface water,glaciers and polar ice caps 2.4%,and other land surface water such as rivers,lakes and ponds 0.6%.Some of the Earth's water is contained within water towers,biological bodies,manufactured products,and food stores.Other water is trapped in ice caps,glaciers,aquifers,or in lakes,sometimes providing fresh water for life on land.