Where is underground water primarily contained?

Underground water is primarily contained in saturated geological formations, often referred to as aquifers. These aquifers are layers of permeable rock or sediment that can hold and transmit water. When rainwater or surface water infiltrates the ground, it moves through these formations, filling the spaces between grains of sand, soil particles, or within fractures of rock.

Saturated geological formations have specific characteristics that allow them to store significant amounts of water, making them vital sources for drinking water supplies, irrigation, and other uses. In contrast, surface reservoirs store water above ground, in contrast to the subterranean conditions of aquifers. The atmosphere, while it contains moisture, does not function as a long-term storage medium for groundwater. Fissures in rocks can indeed hold some water, but they are usually not the primary source for the vast quantities found in aquifers. Thus, the saturated geological formations represent the main repository for underground water.