Edwards Aquifer Studies in Texas

Science Center Objects

The Edwards aquifer in south-central Texas is one of the most productive aquifers in the Nation and is the primary source of water for the rapidly growing San Antonio area. Springs issuing from the Edwards aquifer provide habitat for several threatened and endangered species, serve as locations for recreational activities, and supply downstream users.

The USGS Texas Water Science Center (TXWSC) monitors, characterizes, and models water availability and water quality for the Edwards Aquifer. Visit the links below for more information on our data and science.

The Edwards aquifer in the Balcones fault zone of southcentral Texas is one of the most permeable and most productive aquifers in the world. The competition for ground water from the Edwards aquifer has created some controversial water issues in central Texas. Designated a sole-source aquifer in the San Antonio and Austin areas by the U.S. Environmental Protection Agency (2003), the aquifer is critical to farming and ranching economies west of San Antonio and recreational economies northeast of the city.  Comal and San Marcos Springs and their effluent streams (rivers) support seven Federally listed endangered and one threatened species.

(Source: Conceptualization and Simulation of the Edwards Aquifer, San Antonio Region, Texas)



Real-time USGS data

Estimated Springflow data

EAA Groundwater Monitoring




Edwards Aquifer Recharge Zone

Geologic extent of the Catchment Zone, Unconfined (Recharge) Zone, and Confined Zone of the Edwards Aquifer. (Public domain.)

Forecasting Models

Edwards Aquifer Groundwater Model Uncertainty Analysis

For more information, contact Linzy Foster

TXWSC is undertaking a 1.5-year study to assess parameter and predictive uncertainty in the Edwards Aquifer Authority MODFLOW Model using both linear and non-linear techniques. The Edwards Aquifer Authority (EAA) has recently (2017) updated a numeric groundwater model based on the work of Lindgren and others (2004) and updated by HDR (2011); the model simulates the period from 2001 to 2015 and the drought of record (1947-1958).

Contacts: Linzy Foster



Edwards aquifer recharge zone

Typical limestone formation in the Edwards aquifer recharge zone. (Public domain.)


Hydrogeologic Mapping in Hays County

For more information, contact Ryan Banta

The Texas Water Development Board classifies the karstic Edwards and Trinity aquifers as major sources of water in south-central Texas. To effectively manage the water resources in the area, detailed maps and descriptions of the geology framework and hydrostratigraphic units of the aquifers in Hays County, Tex. are needed. In 2016 and 2018, TXWSC, in cooperation with the Edwards Aquifer Authority, mapped geologic framework and hydrostratigraphy of the Edwards and Trinity aquifers within Hays County, Tex. at 1:24,000 scale.


Rapid recharge to Edwards Aquifer

Seco Creek sinkhole in Medina County, TX provides direct recharge to the Edwards Aquifer. (Public domain.)

Recharge Zone

Edwards Aquifer Recharge Zone Surface-water and Groundwater Interaction

For more information, contact Stephen Opsahl

The effects of urbanization across the recharge zone in Bexar County and potential impact on the water quality in the Edwards aquifer is a topic of specific concern for the City of San Antonio. TXWSC is simultaneously collecting water-quality data from surface-water runoff sites and paired shallow groundwater wells within the recharge zone of the Edwards aquifer to better characterize the water quality connection between surface water and groundwater. 


Edwards Aquifer Recharge Zone Monitoring Network

For more information, contact Stephen Opsahl

TXWSC is implementing a more complete and integrated monitoring network for the Edwards aquifer. More comprehensive and integrated information will improve the understanding of aquifer water quality and establish a baseline for measuring future water-quality changes.


Photo of Spring Lake in San Marcos, Texas

Spring Lake in San Marcos, Texas, is created from hundreds of small springs from the Edwards Aquifer. (Credit: Cassi Crow, USGS. Public domain.)

Water Quality

National Water-Quality Assessment Project in Texas

For more information, contact Marylynn Musgrove or Patricia Ging

Since 1992, NAWQA has been a primary source of nationally consistent data and information on the quality of the Nation’s streams and groundwater. Data and information obtained from objective and nationally consistent water-quality monitoring and modeling activities provide answers to where, when, and why the Nation’s water quality is degraded and what can be done to improve and protect it for human and ecosystem needs. For NAWQA’s third decade (2013–23), a new strategic Science Plan has been developed that describes a strategy for building upon and enhancing the USGS’s ongoing assessment of the Nation’s freshwater quality and aquatic ecosystems.