The largest use of ground water is to irrigate crops. Ground water can be obtained by drilling or digging wells . A well is usually a pipe in the ground that fills the ground water. This water can then be brought to the land surface by a pump. Shallow wells may go dry if the water table falls below the bottom of the well, as illustrated at right.
Water leaving an aquifer is called discharge water .
Water that is pumped from a well is discharge water. Ground water might also discharge naturally as springs or into swamps, lakes, or rivers. Some wells, called artesian wells , do not need a pump. These wells are drilled into an artesian aquifer , which is sandwiched between two impermeable layers. Water enters an artesian aquifer in a permeable recharge zone, which can be miles away from the well.