The
water cycle, also known as the
hydrological cycle or the
H2O cycle, describes the continuous movement of water on, above and below the surface of the
Earth. The mass of water on Earth remains fairly constant over time but the partitioning of the water into the major reservoirs of ice,
fresh water, saline water and
atmospheric water is variable depending on a wide range of
climatic variables. The water moves from one reservoir to another, such as from river to
ocean, or from the ocean to the atmosphere, by the physical processes of
evaporation,
condensation,
precipitation,
infiltration,
runoff, and subsurface flow. In doing so, the water goes through different phases: liquid, solid (
ice), and gas (
vapor).