Water (chemical formula: H2O) is a translucent fluid that forms the world's lakes, streams, rain, and oceans, and is the primary component of the liquids in organisms. As a chemical compound, one water molecule contains one oxygen and two hydrogen atoms which are joined by covalent bonds. Water is a liquid at normal ambient pressure and temperature, but it also co-exists on Earth as ice when it's in the solid state, and in a gaseous state it becomes steam (water vapor). It also exists as fog, dew, cloud, and snow.
Water covers 71 percent of the Earth's surface. It is vital to all known forms of life. On Earth, 96.5 percent of the planet's crust water is found in seas and oceans, 1.7 percent in groundwater, 1.7 percent in glaciers and the ice caps of Antarctica and Greenland, a small fraction in other large water bodies, and 0.001 percent in the air as clouds (formed of ice and liquid water suspended in air), vapor, and rain.