Waterisacommonchemicalsubstancethatisessentialforthesurvivalofallknownformsoflife.Intypicalusage,waterrefersonlytoitsliquidformorstate,butthesubstancealsohasasolidstate,ice,andagaseousstate,watervapororsteam.About1.460petatonnes(Pt)(1021kilograms)ofwatercovers71%oftheEarth'ssurface,mostlyinoceansandotherlargewaterbodies,with1.6%ofwaterbelowgroundinaquifersand0.001%intheairasvapor,clouds(formedofsolidandliquidwaterparticlessuspendedinair),andprecipitation.[1]Saltwateroceanshold97%ofsurfacewater,glaciersandpolaricecaps2.4%,andotherlandsurfacewatersuchasrivers,lakesandponds0.6%.SomeoftheEarth'swateriscontainedwithinwatertowers,biologicalbodies,manufacturedproducts,andfoodstores.Otherwateristrappedinicecaps,glaciers,aquifers,orinlakes,sometimesprovidingfreshwaterforlifeonland.