During periods of little or no rain, the water table may because water use is greater than water recharge.

Water table is the upper level of an underground surface in which the soil or rocks are permanently saturated with water. During periods of little or no rain, this water table may deplete (or dry)  because water use is greater than water recharge. Depletion is a serious threat to the environment because it has several negative effects: increased pumping costs, deterioration of water quality, reduction of water in streams and lakes, or land subsidence.