Aquifers of Texas
The state of Texas covers 23 aquifers (7 major and 16 minor aquifers) that underlie approximately ¾ of the state. The Ogallala Aquifer accounts for about 90% of the water in all of Texas aquifers. Groundwater from Texas aquifers is used for irrigation, municipal use, manufacturing, and livestock production. Pumping of water from many aquifers in Texas has resulted in a significant lowering of the water table.
The major aquifers in Texas include the Ogalalla aquifer, the Gulf Coast aquifer, the Edwards aquifer, Carrizo-Wilcox aquifer, Edwards-Trinity (Plateau) aquifer, the Seymour aquifer, the Hueco-Mesilla Bolson, and the Cenozoic Pecos aquifer. The Ogalalla Aquifer, the largest aquifer in North America, covers 174,000 square miles in 8 states (Texas, Oklahoma, Kansas, Nebraska, New Mexico, Colorado, South Dakota, and Wyoming) and incorporates some of the most important agricultural land in the nation. More than 14 million hectares of land are irrigated by the Ogallala.
Uses of groundwater
In Texas, groundwater is used for irrigation (79.4%), municipal water supplies (13.5%), manufacturing (3.6%), mining (1.4%), livestock (1.2%) and power production (0.9%). The largest source of groundwater in Texas is the Ogallala aquifer whoses water is used for irrigation in the Southern High Plains. The major aquifers are important sources of water for major Texas cities (e.g. Gulf Coast aquifer-Houston, Edwards Aquifer-San Antonio, and Hueco-Mesilla Bolson-El Paso). Many of the the largest municipalities of Texas rely on aquifers to meet their water needs (e.g., San Antonio- 98%), although the reliance on water from aquifers has decreased. For example, in 1990 Harris County (Houston) 71% of water came from aquifer compared to 26% in 2000 and in El Paso reliance on groundwater has decreased from 79% in 1990 to 25% in 2000.
Recharge and water use
Currently, water is pumped from many Texas aquifers much faster than it is being replaced by recharge. For example, 6.2 million acre feet were pumped out of the Ogalla aquifer in 1997 from an aquifer with an average recharge rate of 0.30 million acre feet per year. Pumping water from aquifers faster than they are recharged has resulted in a lowering of the water table which has increased the costs of pumping water from aquifers. Lowering the water table has also resulted in land subsidence, altered underground flow patterns, reduced water quality, and caused many spring to go dry.
Regulation of use of groundwater in Texas
Water law in Texas is complicated in part by the fact that the laws governing the use of groundwater are derived from English law whereas laws governing the use of surface water are derived from Spanish law. Texas gives landowners the "right of capture" of groundwater beneath their property. The state is responsible for overseeing groundwater quality which is regulated by both the Texas Commission on Environmental Quality (TCEQ) and the Texas Water Development Board (TWDB).