aquifer

A body of rock through which appreciable amounts of water can flow. The rock of an aquifer must be porous and permeable (full of interconnected holes) so that it can conduct water. Aquifers are an important source of fresh water, for example for drinking and irrigation, in many arid areas of the world, and are exploited by the use of artesian wells.

An aquifer may be underlain, overlain, or sandwiched between less permeable layers, called aquicludes or aquitards, which impede water movement. Sandstones and porous limestones make the best aquifers.