Subsidence.
There is a limit to how much groundwater can be pumped out of an aquifer without causing depletion of the resource. If more groundwater is pumped out than is naturally recharged by precipitation, the amount of water stored in the aquifer will decline. In some areas, pumping has resulted in subsidence (sinking) of the land surface. Similar conditions may arise from the pumping of petroleum.
Groundwater occupies volume in an aquifer by filling pore spaces between the mineral grains. Because water is essentially incompressible, that water helps support the weight of the overlying rock and soil. When the water is pumped out, the pore spaces may collapse under the load and the volume of the rock and soil decreases. In many areas, that pore space is forever lost; that is, water cannot reenter the aquifer.
Significant subsidence as the result of excessive pumping has been recorded in areas such as:
the Houston–Galveston area of Texas (1 to 2 meters, or 3.3–6.6 feet);
New Orleans (2 meters, or 7 feet);
Venice, Italy (3 meters, or 10 feet);
Mexico City (more than 7 meters, or 26 feet); and
the San Joaquin Valley of California (8 meters, or 26 feet).
Unlike the subsidence caused by cave-ins that result from the collapse of underground mines, sinkholes caused by dissolution of underground carbonate rocks, or human-made sinkholes caused by broken water mains, subsidence as a result of aquifer overdrafting occurs slowly and over a large area. Residents in the region are unlikely to even notice it.