Water can be stored in naturally occuring aquifers, or in tanks and cisterns placed underground. Wells usually take advantage of a preexisting aquifer in order to successfully draw up water from the earth. Once that water has been drawn up, or has been collected via precipitation, it can be stored in a lagoon or cistern for later use. One might store groundwater for a variety of reasons. Agriculture often uses groundwater for irrigation and livestock water.
An aquifers storage is determined by how much water is discharging and being recharged over a period of time. If precipitation comes often and groundwater is only pumped out occasionally, then the aquifer has plenty of time to recharge itself. However, too much usage during times of drought can leave aquifers dry and empty. This can cause lakes and rivers to dry up, and render wells incapable of pumping up water.
