San Antonio and the Edwards Aquifer.


 The Edwards Aquifer is the highest producing aquifer in the state.  Its honeycombed limestone caverns are recharged solely from rainwater falling in the drainage and recharge areas. The Edwards is the sole water source for San Antonio and Suburbs.  As well as being absolutely vital to all humans ever living in the area, it is also home to several endangered animals.  If humans pollute the Aquifer, nothing can use the water. If humans lower the water table through pumping, the springs will go dry and endangered animals will die.  Today humans are pumping so much that the habitats for these animals and our drinking water may be damaged. All of the potential hazards must be addressed in order to assure a reliable water source both now and in the future.

            The foremost hazard to many native species is a lack of natural spring flow.  The Comal springs went dry for nearly five months (144 days) in 1956 and the San Marcos came very close, dropping to only 45.5 cubic feet per second. In a natural setting a drought long enough to cause both springs to go dry would be extremely rare, in fact the San Marcos springs have never gone dry as long as humans in the area have kept records.  This hazard is human based and occurs because this area is no longer in its ”natural” state.  Because of this, the solution must also be human based.   

The Edwards Aquifer Authority began operation on June 28, 1996 with the mission to manage and protect the Edwards Aquifer system, and with a mandate to limit withdrawals.  They are the organization with “powers, rights, and privileges necessary to manage, conserve, preserve, and protect the aquifer”  (EAA Act article 1 section 1.08, 1999).  They have authority over eight of the counties that lie over the Edwards Aquifer recharge and artesian zones; Atascosa, Bexar, Caldwell, Comal, Guadalupe, Hays, Medina, and Uvalde (EAA Act article 1 section 1.02, 1999).  Some counties are not listed by the EAA Act, therefore, the EAA does not have authority over Edwards, Real, Kerr, Bandera, or Kendall counties, even though they are located over the drainage area of the aquifer system.

Besides natural springflow, there are several other sources discharging water out of the aquifer.  Humans use the water for municipal purposes such as drinking, showering, and washing, for agricultural and lawn irrigation, for commercial processes such as beer making and power plant coolant, and for tourism and recreational purposes.  The water pulled out by humans is water not available for natural springflow.  Here is the problem; humans have used the aquifer throughout human inhabitation, but now our increased pumping activities could jeopardize the endangered animals that depend on its spring flow. There are several man made solutions to our man made problems, and one of the most important solutions is through conservation.

The human animal needs to drink less than one gallon of water per day to survive, but in today’s culture we consume on average 176 times that personally for all uses including drinking.  This figure does not include the water used to grow the food we eat, the water used in manufacturing the things we use every day, or the water we use to irrigate our lawns.  The differences between the amount we use and the amount we need represents a significant portion of water and therefore educating people about how to conserve water could reduce overall consumption dramatically.  Both E.A.A. and San Antonio Water System are supplying money and personnel to an education program that shows people how they can conserve water and save money too.

Education alone is typically not enough to significantly reduce water usage.  To “encourage” users to be more conservative, other more direct measures must be taken.  Two such measures are pumping limits and a higher price for water.  The E.A.A. has the authority by statute to issue pumping permits and therefore limiting the amount of total water being pumped.  To reduce the consumption of water throughout metropolitan areas, one solution would be to raise the price of the water.  Right now San Antonio has one of the lowest water prices in the state, which means that it does not cost much to waste water.  The April 2000 water bill for San Antonio Water System users shows that the cost for residential water use is 72.2 cents per thousand gallons (authors water bill).  The average price for water in the United States is $1.30 for every thousand gallons.  This shows that San Antonio’s water rate is almost half of the U.S. average.

 Another method to reduce the water pulled from the aquifer is to recycle it.  Sewage treatment plants are used around the world to treat sewage to a point at which the water can be released into surrounding watersheds.  These plants have recently started to pump their treated water out to some non-potable water users.  Trinity University and several other large water users have taken part in the city’s water recycling program (Purple Pipe Program).  This water is used to water lawns, trees, and often golf courses.  The amount of treated water that is used is theoretically water that no longer needs to be drawn directly from the aquifer.  The Purple Pipe Program is not inexpensive to set up and maintain, but nearly all of the options that actively conserve aquifer water are more expensive than direct withdrawal from the aquifer.  The costs to the users however, must remain the same as the normal water or none would take part in the program.  The program is still in the beginning stages, but there are plans to expand in order to reach new users Eventually, the SAWS recycled water program will supply non-potable water for beneficial use at 20% of the volume that San Antonio currently withdraws from the aquifer annually ( 

Another obvious solution is to increase the amount of water in the aquifer.  This can be accomplished in several ways.  One of the most productive ways to increase the water recharged into the aquifer is through the construction of recharge dams. These structures are built on typically dry creeks and only temporarily capture flood waters and hold them over the recharge zone so the water is allowed more time to percolate through cracks and seep into the aquifer. 

Surface water structures could be constructed as a supplemental water source.  Several of these surface water structures have been proposed, but they have all been rejected as sources for surface drinking water.  One highly publicized proposed structure was voted down twice.  Without getting into economics, there are several inherent problems with the proposed reservoirs.  First, surface water is exposed to evaporation losses, which can become quite significant in hot Texas summers.  Secondly, all of the proposed surface water reservoirs are below San Antonio where the land is fairly flat and reservoirs would be large and shallow.  There are several environmental impacts occurring from large shallow lakes as compared to deeper ones, including higher surface area to volume ratios, which increase evaporation and temperature fluctuation.  The flat terrain also means that more land has to be flooded for an equivalent amount of water. On top of being shallow and evaporating, the water would have to be pumped up-hill to the treatment plant.  Surface water reservoirs are not all bad however.  The bad part is that none of the good ones are being proposed.  The environmental impacts of damning rivers and evaporation losses cannot be avoided, but with proper placement, they can be lessened.  One example is Median Lake to the Northwest of San Antonio.  It is up-hill from San Antonio, so water would not have to be pumped to a treatment plant.  It is deeper so the surface area to volume ratio is less and therefore less evaporation.  The greatest benefit is because of placement.  Some parts of Medina Lake fall over the recharge zone and therefore provide an extra 40,000 acre-feet of annual recharge since 1912 when it was constructed.  A structure such as this is not only a potential source for surface waters, but also because of placement, it acts as a recharge structure and provides the equivalent of about 10% of current aquifer water usage.

Pollution is a second issue of paramount importance to all the organisms that rely on Edwards’s water.  Regardless of water quantity, it would become unusable if it were to fall below a certain quality due to pollution.  Pollution can come from many sources including pesticide and fertilizer runoff, street runoff, gas stations and other forms of chemical storage.  The same structures that allow this aquifer such an exceptional recharge capacity also allow a direct conduit for pollution.  Again these problems occur as a direct result of modern humans.  One of the main threats for pollution is through the development of the areas in the drainage and recharge areas.  This is simple because if there were no humans above the recharge and drainage zones, there would be no real threat of pollution.  Other possible sources for pollution come from the transport of hazardous (even nuclear) waste on roads that cross the recharge and drainage areas, gas stations, and agricultural use of pesticides.  E.A.A. suggests hazardous materials traps and vegetative channels along highways to catch some of the hydrocarbons, radiator fluids, and metal dust from brake linings.  Increased traffic increases risk of accidental spills of hazardous materials. In residential developments, pesticides and fertilizers are common; especially with commercial lawn care companies.  It is estimated that residential developments use 5-8 times agricultural usage.  Some suggestions to reduce run-off include vegetative buffers between lots and creeks (not on homeowner’s lots) which would be maintained by SAWS.   Because it is unrealistic to move everyone off the recharge zone, measures must be taken to reduce pollution.

The potential hazards facing central Texas are great, and the solutions are difficult and often expensive.  What has been done is the formation of a multi-county entity, the Edwards Aquifer Authority.  The EA.A. has the authority to plan out various ways to protect the aquifer and the power to implement and enforce the plans.  What remains to be done is the removal of the bitterness other organizations feel toward this entity, so that the E.A.A. can function properly.





San Antonio and the Edwards Aquifer.


Bryan Hummel

Urban Studies

December 4, 2000


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