Some of the precipitation that falls on land seeps into the ground where it is stored in aquifers and is transported to streams and lakes by subsurface flow. The amount of infiltration is influenced by the permeability and moisture content of the soil, the presence of vegetation and the volume and intensity of precipitation.

The amount of water in an aquifer is indicated by the height of the water table (the upper boundary of aquifer). This animation illustrates the effect of soil permeability (large particles have large spaces between them and let more water in) and precipitation volume (large rain events can lead to more infiltration) on the amount of water stored in the aquifer.