Groundwater is water that has accumulated beneath the Earth's surface in the pores of rocks, spaces, crevices, etc. Groundwater may be meteoric, rainwater having soaked down from above, or juvenile, where water has risen from beneath. Permeable, water-bearing rocks are aquifers; rocks with pores small enough to inhibit the flow of water through them are aquicludes. Build-up of groundwater pressure beneath an aquiclude makes possible construction of an artesian well. The uppermost layer of groundwater saturation is the water table.
A groundwater basin is a geologically and hydrologically defined area that contains one or more aquifers that store and transmit water and will yield significant quantities of water to wells.