Water cycle, also called hydrologic cycle, cycle that involves the continuous circulation of water in the Earth-atmosphere system. Of the many processes involved in the water cycle, the most important are evaporation, transpiration, condensation, precipitation, and runoff...
National Geographic - Hydrologic Cycle
The water cycle describes how water is exchanged (cycled) through Earth's land, ocean, and atmosphere. Water always exists in all three places, and in many forms—as lakes and rivers, glaciers and ice sheets, oceans and seas, underground aquifers, and vapor in the air and clouds...
The hydrologic cycle describes the continuous movement of water above, on, and below the surface of the Earth. The water on the Earth's surface--surface water--occurs as streams, lakes, and wetlands, as well as bays and oceans. Surface water also includes the solid forms of water-- snow and ice. The water below the surface of the Earth primarily is ground water, but it also includes soil water...