An artesian aquifer is a confined aquifer containing groundwater that will flow upwards out of a well without the need for pumping. An aquifer provides the water for an artesian well. An aquifer is a layer of soft rock, like limestone or sandstone, that absorbs water from an inlet path. Porous stone is crushed between impermeable rocks or clay. This keeps the pressure high, so when the water finds a hole, it overcomes gravity and goes up instead of down.