The Edwards Aquifer - San Antonios Primary Water Source

Written by Randy Watson,


So, just what is this Edwards Aquifer that I hear so much about? And why is the level of the Edwards Aquifer important enough to post everyday along with the weather. SAWS, the San Antonio Water System, supplies nearly 2 million people in surrounding San Antonio homes and businesses with clean drinking water, primarily from the Edwards Aquifer. Our area lakes are not used by the City of San Antonio as reservoirs to supply drinking water.

The Edwards Aquifer is an underground body of water with sufficient pressure to be considered an artesian aquifer. Not so much like a river or lake or some other body of water you might think of. (I am by no means any kind of expert on this.) In unscientific terms, it is more like water saturated/pourous/honeycombed rocks, caves, fissures, cracks and crevices deep in the earth. The Edwards Aquifer is said to be one of the largest aquifers in the world. Stretching from just this side of Mexico, through the Texas Hill Country, through San Antonio to the south edge of Austin. Generally running north of US 90 from Bracketville to San Antonio and west of IH35 from San Antonio to Austin. It is about 160 miles long and 5-40 Miles wide.

San Antonio understands the precious resource it has for water and monitors the water levels at the J-17 index well near the National Cemetary at Ft Sam Houston. For instance, today, the water level was measured about 650 ft. (Which is about 81 ft below the surface of the land.) The land surface at the top of the J-17 well is about 731 ft above sea level. They likely have instruments to measure the depth, but they could just as easily drop a string on a weighted cork till they hit water and measure that length of string, then subtract it from the height above sea level. In actuality, this is the hydrologic pressure level of the aquifer above sea level. (The actual Edwards limestone formation is closer around 250 ft above sea level.)

In addition to the water levels of the aquifer being monitored, the springflows that feed the area rivers from the Edwards Aquifer are also monitored. If the flow rate of the springs and/or the levels of the aquifer fall below certain parameters, water saving or Drought Restrictions go into place. We are currently in Stage Two Drought Restrictions, which for residential users means we are limited to 1 day per week during certain hours to water our lawns, wash our cars, water fountains must be off and we must conserve water.

They say our drought will last throughout next year, too. We usually get about 36 inches of rain a year. We are only at 12 inches or so to date, down 15 inches from where we would normally be. Even if it does rain, the rains have to land on the Contribution Zone (click picture to enlarge) in order to fill up the aquifer. The Contribution Zone is north  and west of San Antonio. It pretty much has to rain in the Texas Hill Country. Water then runs down the creeks and streams then drops into the caves and cracks/crevice in the earth in the Recharge Zone. The Recharge Zones are especially sensitive areas, as they are the last chance to keep unwanted runoff (chemicals, pollutants, etc.) from entering our water source.

We value our parks, not only to preserve nature, but to protect our water. Government Canyon State Natural Area, located adjacent to many nice Helotes residential neighborhoods, just outside Northwest San Antonio is a 8,624-acre park mostly drainage area transitioning to the Recharge Zone.

The San Antonio River just bubbles up out of the ground and gets it start from the San Antonio and San Pedro Springs. You can actually see the San Antonio River bubble up out of the ground in the Alamo Heights areas at the "Blue Hole" spring at Incarnate Word University and several other springs at the Witte Museum, San Antonio Zoo, San Pedro Springs Park and Brackenridge Park areas.

Ever heard of fly fishing for trout fishing in Texas? Below Canyon Lake dam they fly fish for trout. Canyon Lake is located 30 miles northeast of San Antinio. Trout require a low water temperature. Sufficient release of water from the Canyon Lake dam provides a stretch of the Guadalupe River below Canyon Lake with a low enough water temperature to support a good population of rainbow trout and a few brown trout as well. In addition to trout, anglers can also catch largemouth bass, smallmouth bass, Guadalupe bass, white bass, and the Rio Grande cichlid.

Interestingly enough, waters from the Guadalupe river provides no significant recharge to the Edwards Aquifer because the stream bed has been cut down below the level of the Edwards limestone. However, seepage losses from Medina Lake do enter the Trinity and Edwards Aquifers. Medina Lake is located 30 miles northwest of San Antonio, while the Medina River flows through Medina County then turn east through south Bexar County to join the San Antonio River in southeast Bexar County and off to the San Antonio Bay at Aransas Natural Wildlife Refuge near Victoria at the Gulf of Mexico.