Texas has numerous aquifers capable of producing groundwater for households, municipalities, industry, farms, and ranches. The Texas Water Development Board (TWDB) recognizes 9 major aquifers − aquifers that produce large amounts of water over large areas (see major aquifers map) − and 21 minor aquifers − aquifers that produce minor amounts of water over large areas or large amounts of water over small areas (see minor aquifers map).
These aquifers are a critical source of water for Texas, supplying 59 percent of the 15.6 million acre-feet of water used in the state in 2003. About 79 percent of this water is used for irrigation, with irrigators withdrawing most of this water from the Ogallala Aquifer alone (82 percent of all groundwater used for irrigation, or 6.0 million acre-feet per year). About 36 percent of water used to meet municipal demands is from groundwater.
The Geologic Atlas of Texas illustrates the surface extent of geologic formations (and aquifers) across the state. The surface extent, or outcrop, of each aquifer is the area in which the host formations are exposed at the land surface. This area corresponds to the principal recharge zone for the aquifers. Groundwater encountered within this area is normally under unconfined, water-table conditions and is most susceptible to contamination. Some water-bearing formations dip below the surface and are covered by other formations. Aquifers with this characteristic are common, although not exclusive, east and south of Interstate Highway 35. Aquifers covered by less permeable formations, such as clay, are confined under artesian pressure. Delineations of the downdip boundaries of such aquifers as the Edwards (BFZ), Trinity, and Carrizo-Wilcox are based on chemical quality criteria.
The characterization of the state's groundwater resources and the development of the maps depicting these aquifers have been accomplished by many staff members of the TWDB over many years. The aquifer maps and reports undergo continual revision to reflect the latest information available.
Aquifers of Texas | TWDB Report 380