The sun's radiant energy is absorbed by the surface, most abundantly near the equator, where sea water is evaporated. Most of the evaporated water returns to the ocean by direct precipitation in the tropics. Moist air also drifts out of the tropics, precipitates as rain or snow, and either returns to the oceans in streams or in groundwater. This image shows a sketch of the hydrologic cycle , which shows the reservoirs and the transfer of water between reservoirs. Groundwater A large fraction of the Earth's fresh water is actually under our feet, in the ground.
Water soaks into the ground through pores between mineral grains and through cracks in rock.
The top of the saturated zone is called the water table . The volume percent of holes in a rock or soil is called porosity . A related property of rock and soil is called permeability , which is a measure of how easily water actually flows though the rock. This table shows the porosity and permeability of some common materials. This picture shows the flow of groundwater in hilly regions.