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How does percolation help form groundwater?

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Diagram illustrating Earth's environmental spheres, with labeled sections showing the geosphere (land and crust), biosphere (living things), atmosphere (air), and hydrosphere (water), each extending vertically from the Earth's surface. — hydrosphere Earth's environment includes the atmosphere, the hydrosphere, the lithosphere, and the biosphere.

Percolation is a critical process in the hydrologic cycle that facilitates the formation and replenishment of groundwater.12

The process begins when precipitation reaches the Earth's surface and infiltrates the soil. Once the soil moisture zone becomes saturated, gravity pulls the excess water downward through the unsaturated, or vadose zone. This downward movement of water through the soil and geologic strata is known as percolation.134

As water percolates, it eventually reaches the water table, which marks the upper boundary of the zone of saturation. By moving into these deeper layers, the water replenishes aquifers—underground reservoirs that store water within the void spaces of soil and rock. This replenishment process is referred to as recharge. In addition to transporting water, percolation often acts as a natural filtering process, helping to clean the water as it passes through the ground.1325