Forms available to life: Liquid water is the primary phase in which water is used, though some organisms can harvest water vapor.

Reservoirs: The oceans contain 97$ of the water in the biosphere. About 2$ is bound in glaciers and polar ice caps, and the remaining 1% is in lakes, rivers, and ground water.

Key processes: The main processes are evaporation of liquid water, condensation into clouds, and precipitation. Transpiration by plants also moves significant volumes of water. Surface and groundnwater flow can return water to the oceans.