Water is a chemical compound with the formula H₂O, consisting of two hydrogen atoms covalently bonded to one oxygen atom. Its bent molecular geometry (104.5° bond angle) and high electronegativity difference produce a strong dipole moment, hydrogen bonding, and the anomalous thermal and solvent properties on which all known life depends. Water exists naturally on Earth as solid, liquid, and gas, and covers approximately 71% of the planet's surface.

A drop of water falling toward water in a glass Credit: José Manuel Suárez from Spain (CC BY 2.0).
A drop of water falling toward water in a glass Credit: José Manuel Suárez from Spain (CC BY 2.0).
This pillow basalt on the seafloor near Hawaii was formed when magma extruded underwater. Other, much older pillow basalt formations provide evidence for large bodies of water long ago in Earth's history. Credit: National Oceanic and Atmospheric Administration (Public domain).
This pillow basalt on the seafloor near Hawaii was formed when magma extruded underwater. Other, much older pillow basalt formations provide evidence for large bodies of water long ago in Earth's history. Credit: National Oceanic and Atmospheric Administration (Public domain).