An aquifer is a body of rock, often sandstone or limestone, that contains significant quantities of water that can be tapped by wells or springs. Much of the human population depends on aquifers for its water supply.
An artesian aquifer is an aquifer in which ground water is confined under pressure significantly greater than atmospheric pressure. This pressure, called artesian pressure, is generally due to the weight of water at higher levels in the same zone and is sufficient to cause water to rise above the level of the aquifer in a well or natural fissure. An artesian aquifer is bounded above and below by confining beds of less permeable rock.