Our Drinking Water
The Edwards Aquifer provides drinking water for over 1.7 million people in Central Texas. San Antonio pumps aquifer water from the Southern segment of the Edwards Aquifer. Over 50,000 people in the Austin area rely on the Barton Springs segment of the Edwards Aquifer. Barton Springs and Barton Creek also contribute water to the City of Austin’s municipal supply.

Growing population along the Edwards Aquifer watershed is putting pressure on ground water supplies. Over-pumping of the Edwards and Trinity aquifers threatens to reduce and potentially dry up springs and rivers, jeopardizing the existence of rare species and the health of local and coastal economies – and of our drinking water.

Increasing urban development of the Edwards Aquifer is increasing contaminant loads in the public’s drinking water. Frequently, local governments award subsidies to developers building large scale projects over the aquifer.

A proposed golf course/hotel/residential development outside San Antonio on the Recharge Zone of the Southern Edwards Aquifer ignited the citizens of San Antonio to rally to protect their drinking water. The motto of their campaign: “Not on Our Aquifer; Not with Our Money!”

To protect this invaluable and irreplaceable resource, we advocate for the following:

  1. Repeal the Rule of Capture that allows groundwater to be mined beyond the limits of sustainability and empower local ground water districts to protect spring flows.
  2. Encourage rain water collection to reduce dependence on groundwater and eliminate need for surface water extensions that spur high density development over the aquifer.
  3. Reduce consumption of water through native landscaping, rebate programs for low water use appliances, and specific goals for reduced consumption. Reduced consumption can eliminate costly new water treatment plants, transmission systems, and reservoirs – saving taxpayers’ money.

Visit Save the Aquifer for more on what you can do to help save our drinking water – the Edwards Aquifer – from over-pumping and contamination.

The Environmental Protection Agency of the United States designates Sole Source Aquifers when drinking water for a given service area is a “sole or principal source” of water. That is, an aquifer which is needed to supply 50% or more of the drinking water for that area and for which there are no reasonably available alternative sources should the aquifer become contaminated. The Edwards Aquifer Ecosystem of Central Texas is one of our most valuable, irreplaceable and endangered public treasures.

The Greater Edwards Aquifer is known as a karst aquifer, characterized by rapid, open-channel water flow and by a thin to nonexistent soil cover. Because of these physical factors, the Texas Commission on Environmental Quality has recognized since 1989 that the Edwards Aquifer is more vulnerable to pollution than any other major aquifer in Texas. Visit Geology and Hydrology for more.


Great Springs and Rivers
The Edwards Aquifer is a mysterious maze of underground rivers, chutes, and rivulets that provides the essential source of life for most of the residents of Central and South Central Texas. Most of the Edwards Aquifer is hidden to all but a relatively few trained geologists, water engineers and cave enthusiasts. However, many are familiar with its prolific springs that emerge along the ragged edge of the Hill Country.

Known as “Great Springs,” these springs nourished native peoples for thousands of years. Beginning in the early 1700s, European immigrants settled around the Great Springs, utilizing their flows for milling, irrigation, fishing, drinking, recreation, and religious purposes. In the following 300 years, the Great Springs sustained the development of all of the major cities in central and south central Texas. From northeast to southwest, the largest of the Great Springs of the Edwards Aquifer are:


Salado Springs
The historic Stagecoach Inn, on the east side of Interstate 35 at Salado, was located just above Salado Springs, the 12th largest in Texas. Salado Springs are the major outflows from the northern segment of the Edwards Aquifer.

Barton Springs
Texas’ capital city was located on the banks of the Colorado River in part because of the reliable and abundant flows of Barton Springs, the 5th largest in the state. Located in Austin’s Zilker Park, Barton Springs Pool is open for swimming all year, with free swimming in winter months.

San Marcos Springs
The San Marcos Springs are the 2nd largest in Texas. The San Marcos River begins at the springs on the campus of Texas State University and flows through the City of San Marcos park system. The river is popular for snorkeling, diving, inner tubing, canoeing, kayaking and swimming.

Hueco Springs
Hueco Springs, the state’s 7th largest, flow into the Guadalupe River at the well-known Hueco Falls rapid, 3.5 miles upstream of Gruene, the inner-tubing capital of Texas.

Comal Springs
Emerging in New Braunfels’ historic Landa Park, Comal Springs are the largest in Texas and the southwest United States. Landa Park’s spring-fed pool and the Schlitterbahn water park a short distance downstream on the Comal River are enjoyed by hundreds of thousands of Texans every year.

San Antonio Springs
Historically the state’s 6th largest, San Antonio Springs emerge on the property of the Incarnate Word Sisters north of downtown San Antonio in a preserve known as the Headwaters Sanctuary. From here they flow through Brackenridge Park into downtown San Antonio and down along the string of Spanish Missions. Spanish missionaries located here in 1718 in large part because of the abundant pure water provided by the springs; the City of San Antonio followed. Today, San Antonio is the largest city in North America wholly dependent on groundwater, and thus the future of the city depends on sustainable management of the Edwards Aquifer

San Pedro Springs
Located a short distance north of downtown San Antonio, San Pedro Springs emerge in San Pedro Park, the second oldest public park in the United States (next to Boston Commons). San Pedro and San Antonio Springs emerge at relatively high elevations in the Edwards Aquifer and have suffered drastically reduced flow due to heavy pumping by cities and farmers in the southern Edwards region.

Leona Springs
This large group of springs is the source of the Leona River and supported the development of the town of Uvalde.

Las Moras Springs
Emerging at Brackettville in Kinney County, these Springs are also known as Fort Clark Springs; they are the 11th largest in Texas and emerge in a swimming pool shared by the surrounding residents.

San Felipe Springs
Fed by the Edwards and other limestone formations, Texas’ 4th largest springs provide the water supply for the City of Del Rio. Emerging just north of Highway 90, San Felipe Creek flows 24 miles to the Rio Grande.

Goodenough Springs
Historically Texas’ 3rd largest, these springs are now covered by Amistad Reservoir on the Rio Grande. Fed by Edwards-associated limestones and other formations, the pressure head from the reservoir has reduced flow considerably.

These Great Springs, and the patterns of settlement which they engendered, have been shaped by forces more than 100 million years old, from a time when the sea covered almost all of what is now Texas. Over the eons, the calcium carbonate shells of marine organisms that lived in this shallow sea accumulated hundreds of feet thick, forming the Edwards, Trinity and other associated limestones. The sea made its final retreat 60 million years ago, and terrestrial life forms took over.

Texas Geology and Hydrology
The limestone hills, clear running streams and creeks, and prolific springs and rivers that we see today are the result of millions of years of geologic forces, from a time when the sea covered almost all of what is now Texas. Over the eons, the calcium carbonate shells of marine organisms that lived in this shallow sea accumulated hundreds of feet thick, forming the Edwards, Trinity and other associated limestones. The sea made its final retreat from what is now the land of Texas 60 million years ago, and terrestrial life forms took over.
Seventeen million years ago, the earth shifted, breaking and lifting a large piece of this coastal plain 300 to 1,200 feet up, along what is now called the Balcones Fault zone. This line of uplift – beginning north of Waco and arching south and then west to near Del Rio – marks the boundary between the forested limestone Hill Country to the north and west and the gently rolling Blackland Prairie and Texas Coastal Plain to the east and south.

Over time, the forces of erosion carved what we recognize as the flat-top, stair-stepped Hill Country out of the uplifted limestone of the Edwards Plateau. Millions of years of slightly acidic rain percolated down through the faulted and fractured limestone, dissolving the rock and creating spaces that hold and convey water. These spaces range from tiny “honeycomb” pores to large caverns. Many of the largest of these caves are now open for touring.

Water coursing into the aquifer eventually eroded flow paths for water to move through. These open channels allow water to move through the aquifer very rapidly and only minimally filter the water. Studies in which non-toxic dye is injected into the aquifer have revealed that water can move up to 8 miles per day underground through the Edwards. This is far faster than, for example, a sandstone aquifer where water sometimes moves only centimeters per year. This means that if pollutants enter the Edwards Aquifer, they will not be naturally filtered before the water emerges at the Great Springs or in people’s drinking water wells.

The exposed limestone on the surface of the Balcones Fault Zone, known as karst limestone, features numerous caves, sinkholes, faults and fractures where rain fall and creek and stream flows can enter the underground Edwards Aquifer. This is also known as the Recharge Zone because this is where the aquifer is “recharged” with fresh water from contributing water bodies, caves, and sinkholes.

North and west of the Recharge Zone is the Contributing Zone, which consists of Hill Country watersheds that contribute water to creeks, rivers, and streams that flow across the Recharge Zone. The quantity and quality of water leaving the Contributing Zone affects the quantity and quality of water that enters the aquifer in the Recharge Zone.

The large flowing springs of the Edwards Aquifer exist where the hydraulic pressure is sufficient to force water up through faults to the surface. Confining layers of rock that does not easily transmit water trap groundwater, allowing pressure to build. Major natural discharge occurs at Salado Springs in Salado, Barton Springs in Austin, San Marcos Springs in San Marcos, Comal Springs in New Braunfels, Las Moras Springs in Brackettville, and San Felipe Springs in Del Rio. San Antonio Springs and San Pedro Springs in San Antonio are dry most of the time because large amounts of water are pumped from the ground by users in Bexar county, but they flow when Aquifer levels are very high.

In general, the movement of groundwater in the freshwater part of the Aquifer is from areas of higher elevation in the southwest toward major discharge areas in the northeast. The flow pattern is controlled primarily by the locations of barrier faults that disrupt the continuity of the permeable Edwards strata. The presence of many faults and fractures makes the flow patterns highly complex. Groundwater divides exist in the west near Brackettville and in the east near Kyle, so the San Antonio segment of the Aquifer is hydrogeologically separated from Edwards limestones on either side. For example, Barton Springs in Austin is also an Edwards water feature, but because of the groundwater divide near Kyle, waters in that portion of the Aquifer do not mix with waters in the San Antonio segment, where most of the use takes place.

The text above is largely based on Gregg Eckhardt’s work that is available at www.edwardsaquifer.net.

Plants and Animals of the Edwards Region
The Edwards Aquifer ecosystem is blessed with more than 60 species of plants and animals that live here and nowhere else in the world. Blind salamanders, catfish, crustaceans, and other “cave critters” have evolved in isolated habitat “islands” within the aquifer, in the dry caves above the water table, and at the Great Springs. The Barton Springs and Austin Blind salamanders live only at Barton Springs, Texas Wild Rice and the San Marcos gambusia live only in the San Marcos River, and the Texas Blind salamander is known only from a few caves that reach into the Southern Edwards Aquifer.

The Edwards Aquifer Ecosystem has such a diversity of wildlife that it is on a global list of biodiversity “hot spots” deserving the immediate attention of conservationists. New species are still being discovered, right here in the backyard of major research institutions like the University of Texas, Texas A&M, and Texas State University.

Distinct Hill Country plant communities are characterized by mixed oak and ashe juniper woodlands, oak savannah and shinnery, wildflowers, native grasses and riparian woodlands. Several centuries of farming and ranching have altered the landscape, but the ruggedness of the Hill Country has assured that many of the native plants and animals have survived. For example, mature oak and ashe juniper woodlands provide nesting habitat for the endangered Golden-cheeked Warbler, a small migratory songbird that is the only bird species (out of 590 that come through Texas) entirely native to Texas.

Many of the plants and animals unique to the Hill Country are listed as “threatened” or “endangered” by the U.S Fish & Wildlife Service because they have extremely limited ranges which are being destroyed by rapid urbanization, urban runoff pollution, and/or excessive water withdrawals. The threat of extinction to sensitive fish, salamanders and other species that live in the Edwards Aquifer and its Great Springs is particularly acute.

Conservation measures that will sustain these endangered species will assure that the Aquifer and Springs are sustained for human use and enjoyment as well.

Fountain Darters

Fountain Darters

Aquatic Species
Through a process known as “parallel evolution,” the salamander species from different spring outlets are distinct species, but resemble not just each other but also salamanders found in karst limestone aquifers in other parts of the world. All of these Edwards Aquifer aquatic salamander species are known as “neotenic,” meaning they reproduce in the aquatic form and do not metamorphose into a terrestrial adult form (a trait most amphibians are known for). If their springs become polluted or pumped dry, they cannot walk on land to find another place to live.

A number of fish species have evolved both within the aquifer and in the spring outflows. These species include the Texas Blind catfish, which only lives deep within the San Antonio segment of the aquifer; the Fountain Darter and San Marcos gambusia from the San Marcos River, and the recently discovered San Felipe gambusia.

Troglobites (Cave Dwellers)
The largest group of species unique to the Edwards Aquifer Ecosystem consists of cave-dwelling invertebrates. These include insects, crustaceans, spiders, bugs, and other small “cave critters.” Many are terrestrial, living in limestone caves above the water table, and are known from one to only a few caves. The isolated cave networks that dot the Edwards and associated limestones–like the large springs–are isolated from each other and thus have provided laboratories for the evolution of unique life forms.

Plant Species
A number of interesting and at-risk plant species also live in the Hill Country. Perhaps best known (and at greatest risk of extinction) is the Texas wild rice, which lives in the upper reaches of the San Marcos River and no where else in the world. The Bracted twistflower and the Canyon mock orange are also plant species threatened with extinction.

austin-blind-salamander barton-springs-salamander

Caves of the Edwards Aquifer
Texas has some unusually beautiful and interesting show caves to offer. Several other caves are now open to guided “Wild Caving Tours.”

caves-cascade-cavernsCascade Caverns

Located between San Antonio and Boerne, Cascade Caverns’ tour follows the main 244-m-long passage, which steadily enlarges until ending in a large room highlighted by the historic cave’s namesake – an impressive waterfall.

caves-c-without-a-nameCave Without A Name
Located northeast of Boerne, Cave Without A Name has a short trail but is a wonderful cave. A staircase spirals down a pit and opens into a 7-m-high by 12-m-wide passage decorated with large speleothems. The trail ends after 186 m at a large stream passage.

caves-sonoraCaverns of Sonora
Near Sonora off IH-10, Caverns of Sonora is internationally recognized as one of the most beautiful caves in the world. Its basic layout is a complex 3-dimensional maze formed along a few parallel or near-parallel fractures. Most of the passages are lined with sparkling speleothems.

caves-inner-spaceInner Space Cavern

In Georgetown off IH-35, Inner Space Cavern is a large, complex cave with many beautiful formations and interesting displays of Pleistocene-age mammal bones. Visitors enter the cave on a cable car ride and the trail is smooth and sloping, about 550 m (1,800 ft.) long.

caves-longhorn-caveLonghorn Cavern
Between Burnet and Marble Falls off Hwy 281, Longhorn Cavern has few formations but lovely wall sculpting and large calcite crystals. At different times the cave was a Comanche hideout, a black powder factory, a dance hall, a restaurant, and a church.

caves-nat-bridge-cavernNatural Bridge Caverns
Near New Braunfels off IH-35, Natural Bridge Caverns is the largest Texas show cave and one of the most impressive because of its size and beauty. The cave has massive formations, including totem poles, fried eggs, stalagmites, and a flowstone floor.

caves-wonder-caveWonder Cave
In San Marcos off IH-35, Wonder Cave is unusual in that it is formed along a fault in the Balcones Fault Zone. The cave is historic in that it is the smallest and oldest continuously operating of the seven show caves in Texas and is now part of the Wonder World theme park.

caves-braken-bat-caveBracken Bat Cave
Just outside San Antonio, off IH-35 near Garden Ridge, Bracken Cave is home to the world’s largest bat colony. Each year, some 20 million Mexican Free-tailed bats gather there to give birth and rear their young. Their emergence from the cave each evening is one of the most spectacular sights in nature. You can see this breathtaking bat colony by becoming a member with Bat Conservation International.

caves-frio-bat-caveFrio Bat Cave
South of Concan, the Frio Bat Cave houses the 2nd largest Mexican Free-tailed bat population in Texas. There are 2,000 feet of cave, with an estimated 10 million bats. The interpretive tour guide will share his knowledge about bats and the history of the cave dating back to the Civil War. You can watch as hawks and falcons catch bats for their evening meal.