aquifer

an aquifer is a geological formation (or sometimes part of a formation or a group of formations) that contains saturated material of sufficient permeability to yield ‘useful’ quantities of water to wells and/or springs. An aquifer may be confined or unconfined. Unconfined aquifers can receive direct recharge from rainfall infiltrating and percolating through the unsaturated (or vadose) zone down to the water table. Confined aquifers are separated from the surface by impermeable materials and cannot be recharged directly by rainfall.