Forces of Nature: ThinkQuest 2000 (Team #C003603)
http://library.thinkquest.org/C003603/english/droughts/thehydrologiccycle.shtml
Water flows in a pattern known as the hydrologic cycle. This is the process in which water is recycled from the land to the oceans to the atmosphere and back to the earth again. Water exists in three forms - as a solid (ice), a liquid (water), and as a gas (water vapor). Water from the ocean is evaporated (or turned from liquid into vapor) into the air. Warm air near the ground rises, and as the water vapor is carried into the colder layers of our atmosphere, they condense and fall back to earth as rain, hail, sleet, or snow. The rain that falls to the earth seeps through the ground or is carried in rivers and streams to the oceans, where the cycle repeats.