A hydrosphere is the total amount of water on a planet. The hydrosphere includes water that is on the surface of the planet, underground, and in the air. A planet's hydrosphere can be liquid, vapor, or ice.
The hydrosphere is one of the four spheres of the Eart system; the other three are the geosphere or lithosphere (solid rocky part of Earth), atmosphere (gases surrounding Earth), and biosphere (living things).
