The common name for the chemical compound water is simply "water," with the chemical formula H₂O. Water is essential for all forms of life; it serves as a solvent, a reactant in biological reactions, and plays a key role in temperature regulation within organisms. It is vital for metabolic processes and is involved in the transportation of nutrients and waste in living cells. Water exists in three states—liquid, solid (ice), and gas (water vapor)—and covers approximately 71% of the Earth's surface, primarily in oceans, rivers, and lakes.