water (H2O) /wô″tər/ [AS, waeter] , a chemical compound, one molecule of which contains one atom of oxygen and two atoms of hydrogen. Almost three quarters of the earth’s surface is covered by water. Essential to life as it exists on this planet, water makes up more than 70% of living things. Pure water freezes at 32° F (0° C) and boils at 212° F (100° C) at 760 mm Hg.
