The water that fills cracks, voids, and other openings in beds of rocks, sand, and soil is called groundwater. It is found in soils and sands that are able to retain the water — much like a sponge holds water — and is constantly replenished by rainfall or snow. Texas is blessed to have extensive groundwater resources. There are nine major aquifers (from which the groundwater is pumped) and 20 minor aquifers in the state, storing between three and four billion acre-feet of groundwater. Most areas of the state can draw water from one or more of the aquifers.
Unlike surface water, which can be severely polluted and must be treated before it’s ready to drink, groundwater pumped from deep wells is naturally filtered by the sands. Once it’s chlorinated, in most cases it’s ready to go (unless it has been contaminated by some other source).
Once considered limitless, groundwater levels can decrease as a result of excessive pumping. Each year, out of all the rainfall, only about 5.3 million acre-feet are absorbed and “recharge” into the state’s aquifers. As you can see from the chart below, in 1996 the 9.9 million acre-feet of groundwater pumped exceeded the natural recharge, for a net loss of 4.6 million acre-feet of groundwater — a loss that cannot be restored.