The continuous process by which water is circulated throughout the Earth and its atmosphere. The Earth's water enters the atmosphere through evaporation from bodies of water and from ground surfaces. Plants and animals also add water vapor to the air by transpiration. As it rises into the atmosphere, the water vapor condenses to form clouds. Rain and other forms of precipitation return it to the Earth, where it flows into bodies of water and into the ground, beginning the cycle again. Also called water cycle.
The continuous circular process in which the water of the Earth evaporates from the oceans, condenses, falls to the Earth as rain or snow, and eventually returns to the oceans through run-off in rivers or streams. Some water is absorbed by plants and returned to the atmosphere as vapor.