Water
Water is one of the Earth's basic naturally occurring elements. It covers about 70% of the world's surface, and is one of the key parts to the survival of species. Up to 60% of the human body is water!
Scientific Makeup
Chemically, water(H2O) is two atoms of Hydrogen, and one atom of Oxygen. Water by definition is usually a liquid, although it can be converted to different states by the removal or addition of heat. Water heated to 100 degrees Celcius (the boiling point) begins to convert to steam, a gaseous state, and when cooled to 0 degrees Celcius (the freezing point) converts to ice, a solid state. Water is unique in that it is the only naturally occurring substance that is found in these three states.
Additionally, water is usually referred to as "the universal solvent" because of its ability to dissolve more substances than any other existing liquid. It has a neutral acidity, which on a pH scale has a measurement of 7.
Uses
The availability of water on the Earth affords humanity an incredible number of uses, aside from consumption as an integral part of survival. Water can be used to cool machinery and facilities, such as nuclear power plants and industrial milling tools. Water can also be heated to create steam--the focus of the steam engine which was born out of the industrial revolution. High pressure water jets can also be used to cut through steel and concrete.