The water cycle , or hydrologic cycle , is one of the most important processes to living organisms on Earth. Water is able to absorb and retain heat, producing stable temperatures important to life. Water is the medium in which all chemical reactions occur in cells. Water transports gases, minerals, and nutrients within living organisms. Water transports minerals and nutrients geographically, and also plays a role in controlling climate.
Water is the medium in which much of life exists - streams, rivers, ponds, lakes, and oceans.
These are some of the major ways in which water plays a central role in life. Living organisms cannot go without water for very long. For most humans, this period is somewhere around 2 or 3 days at the most. The water cycle depicts the major processes involved in the exchange of water between the atmosphere and the Earth's largest reservoirs - the oceans, the lakes and rivers, and the groundwater. Water that has evaporated into the atmosphere condenses and falls as precipitation - either rain, snow, sleet, hail, or fog that condenses on colder surfaces.