Frequently Asked Questions

Here are answers to some of the questions I get asked most frequently regarding the Edwards Aquifer and issues surrounding it. Let me know if you have a question you would like to see answered here!

Will we run out of water?

Unless we start mining the resource by using more than goes in on a long term basis, we will always be able to get plenty of good water for critical uses like eating and bathing.  We have never seen the Aquifer less than 90-95% full, so there is lots of water down there we can use if we have to in an extreme drought.  However, we sometimes DO run out of water in the top 5-10% of the Edwards formation, and when that happens the springs stop flowing.  Lots of people, along with endangered plants and animals, depend on water from the springs.  To keep them flowing we have to keep the Aquifer almost full.
Do we have a water shortage?

Maybe it's more correct to call it a money shortage.  If money were no object, we could do very expensive things like desalinate ocean water and have an unlimited supply.  What we are running short on is the cheap, seemingly limitless aquifer water that we have been used to using without restriction.  All of the alternative water sources seem very expensive by comparison.  
So is our water shortage more related to environmental protection and economics and equitable sharing than an actual physical shortage of water?

Yes.
How much water is in the aquifer?

Because of the complexity of the Aquifer system, it is difficult to narrow down the range of how much water we think it contains.  One thing that is clear is there's a big difference between how much water the Aquifer contains and how much water could be extracted.  Some researchers have estimated the Aquifer may contain as much as 175 million acre feet.  However, that figure includes water locked up in pore spaces that are not connected to any other pores, so that water can't move anywhere and is therefore not available.  A more reasonable estimate of 25-55 million acre-feet is based on effective porosity, which is a measure of the percentage of pore spaces within the rock that are connected to other pore spaces (see Maclay, 1981 and Ogden, 1986).   Pores must be connected for water to move through the rock and to the surface through springs and wells.  Additionally, one should not picture the Aquifer as a vast underground pool.  There are undoubtedly many large caverns, but most of the water is in small pore spaces that are probably no larger than your finger.
Some people say there is enough water in the aquifer to supply our needs for several hundred years, even if it never rains again. Is that true?

If there's 25-55 million acre feet of water available, and if we use only 450,000 acre feet a year, then it sounds like there's enough water to last 200 years!   However, the aquifer contains a lot of water that we can't really get to in legal or practical terms.   The problem is the springs go dry when the aquifer is still 95% full.  So as long as we are going to maintain at least minimal natural springflows for the sake of endangered species, recreational economies, downstream ecosystems, and downstream economies, then the large amount of water below the level of the springs is essentially unavailable to us.  Even if we did decide to let all the springs go dry and pump out as much water as we need, it is very expensive to pump large amounts of water up from great depths and it would soon get prohibitively expensive.
If the problem is the springs go dry, why can't we artificially augment springflows?  Is that feasible?

Proponents of springflow augmentation argue that if we can keep the springs flowing artificially, endangered species would be protected and we might be free to draw the Aquifer down below the level of springs.  This would increase the amount of water that is available to us and allow us to utilize the Aquifer to a greater capacity as a reservoir.  McKinney and Sharp, 1995 studied the technical feasibility of augmenting springflows and concluded that artificial supplementation could provide protection in times of drought for federally protected species, but a lot of unknowns still exist.  Other analysts are concerned that augmentation might be prohibitively expensive and that systems to deliver water to the springs might provide little or no benefit when needed most, during times of extended drought.
 
On one side of the issue, proponents argue that artificial augmentation at least deserves a fair and impartial evaluation, which has not been completely done.  Opponents argue that artificially augmenting springflows is like robbing Peter to pay Paul...the water has to come from SOMEwhere, and the source would probably be the Edwards Aquifer.  The endangered species prefer the chemistry and temperature of Aquifer water, so water from surface water or other sources might not suffice.  Besides, opponents say, artificially augmenting springflows completely misses the point....what is desired is natural springflow.
 
The 1995 study looked at injecting water into the Aquifer near the springs; enhancing local and regional recharge; and direct addition to the surface at the spring openings.  Sharp said further studies could answer a lot of unknowns, such as specific flow paths to the springs and whether any of the aquatic species require water to be flowing from the spring orifices.  Those studies are not being done, because "people are afraid of the answers," Sharp said.
 
Some say that we should manage the Aquifer as a reservoir.  Will that solve the problem?

Proponents of managing the aquifer as a reservoir suggest there are many ways we could use the Aquifer to a greater extent in dry times, and then let it fill back up when the rains come.  This is certainly the approach that water managers use to get the maximum benefit from a surface water reservoir.  Such an approach could involve recirculation and/or augmentation systems to keep the springs flowing.  A number of studies are underway regarding Aquifer optimization, and many are focused on gaining a better understanding of the flowpaths and discrete units or "pools" within the Aquifer.  
 
It might be possible, for example, to draw more water from particular units while leaving springflows largely unaffected.  Or it might be possible to bring water from behind the "Knippa Gap", which is a narrow opening within an extensive, complex system of barrier faults and a major controller of flow within the Aquifer.   Huge amounts of water cannot pass quickly through the Gap, so water piles up in storage units behind it, causing water levels in wells to the west to display much less variability than wells to the east.  Water that recharges in western Medina and Uvalde counties has to flow through the gap to reach the main freshwater zones in Medina and Bexar counties.   
 
Many questions are unanswered.  For example, there is no evidence to suggest that recharge will be increased during rainy times simply because we have drawn the level down low in dry times.  The recharge conduits are fixed in size and may not be able to recharge the same volume of water drawn out.  
 
What about putting more water into the Aquifer?  Will building recharge dams help?

Though many questions and issues exist, there is indeed some potential to build a few Type II recharge dams in addition to the ones that already exist.  They would not be a magic-bullet type of solution and could only supply a small percentage of overall projected water needs.  The draft plan of the South Central Texas Regional Water Planning Group estimates an average of 21,000 acre-feet per year could be added to the Aquifer.  In short term droughts additional recharge could help get us over the hump, but recharge dams can't help in a long term drought because there will be no water to recharge.  The Edwards is not a good storage aquifer where water stays put for use tomorrow.  As long as enough hydraulic pressure exists to force water up of the level of springs, significant amounts of water will flow out.  In a 3-5 year drought, all the water that was recharged during wet times will have left the Aquifer.  And there are some thorny issues involved, such as the fact that Type II dams are constructed on the recharge zone which is the most environmentally sensitive area.  Also, most people don't want their land to be sacrificed for such projects, but somebody's would have to be.  Further, it is unclear who would pay and who would benefit.  For more on recharge dams, such as what the difference is between Type I and Type II dams, see the section on Edwards Alternatives. 
I've heard that if the Aquifer goes low,  salt water would intrude into the fresh water areas.  Is that true?

The US Fish & Wildlife Service includes the possibly of salt water intrusion into the fresh water zone among the reasons that some species have been listed as endangered, but I have never talked to a hydrologist who felt that saline water intrusion was anything to be even remotely concerned about.  During dry times or when the Aquifer is drawn down to low levels, very small volumes of salt water might intrude along the interface between the fresh and saline sections of the aquifer, but the saline water would be flushed back out again quickly when water levels rose.  A study by Ewing and Wilbert, 1991 concluded that water quality deterioration, in all cases except actual ground-water mining, would be temporary and limited largely due to the significant difference in permeability between the fresh and saline sections of the aquifer and to the flushing action that would occur with renewed increase in recharge.  The reason the water is saline to begin with is because the rock in that area is much less permeable, so water moves slowly and stays in contact with the rock for a long time.  Because the saline water is tied up in the rock, it will be difficult for it to move from that area.  Also, the saline zone lies downhill from the fresh water zone, and it seems very unlikely that salt water would suddenly start to run uphill toward the fresh water zone.  Additionally, salt water is more dense than fresh water, so it tends to sink below fresh water and the two do not readily mix.
What exactly is this "bad water line" that separates the fresh water from the salt water?

The fresh water / saline water interface, usually known as the "bad water line" is the convergence of two flow systems within the Aquifer.  It is actually a zone and not a line.  The freshwater area is generally updip, closer to the land surface; while the saline water area is farther downdip, deeper underground.   In the freshwater portion of the Aquifer, the limestone is highly permeable and transmission rates are high, so water moves through it relatively quickly.  By contrast, deeper down in the formation, the saline water portion of the Aquifer has low transmission rates and much higher residence times.  When water is in contact with limestone, it continually dissolves mineral solids from the surrounding rock matrix.  Eventually, the concentration of total dissolved solids (TDS) becomes greater than about 1000 ppm, and the water is considered saline and not drinkable (seawater is about 33,000 ppm).  The "bad water line" is a natural phenomenon that occurs along the southern and eastern edges of the fresh water zone where water has been in contact with limestone for a long time.  Since the rock in the saline water zone is less permeable and does not transmit water as easily, the movement of water is slower.  As a result, water stays in contact with limestone longer and becomes more saline.
How old is water in the Aquifer?

Because the movement of water in the Aquifer is highly complex, the waters we pump from the ground and drink are a mixture of waters of many different ages.  In some places water moves only a few feet a day, but in other places water may move 1000 feet a day (see Maclay, 1981 and Ogden, 1986) .  The average residence time for water in the aquifer is around 200 years.
How much water goes into the Aquifer each year?

Average annual recharge for the period 1934-2005 is about 719,000 acre feet.  However, averages do not mean that much in this region...recharge is highly variable from year to year (see recharge chart).
Does the Aquifer filter water?

The Edwards provides treatment that would otherwise cost us billions of dollars.  Whether or not it is a filter depends on which definition you like.  According to Webster's dictionary, a filter is "a porous article or mass that serves as a medium for separating from a liquid or gas passed through it matter held in suspension or dissolved impurities or coloring matter."  In the field of water treatment, a filter is usually composed of paper or sand, where pore spaces are small enough so that water will pass through but small suspended particles will not.  The Aquifer is not what people in the water resource field traditionally think of as a filter.  However, there are many pore spaces within the Aquifer that are so small that large suspended particles cannot pass through.  In this sense, and according to a strict definition, the Aquifer is indeed a filter and does provide some filtration. 
 
Regardless of what one thinks is a filter, there's one thing for sure:  the Aquifer transforms dirty brown polluted recharge water into crystal clear spring water and well water that we safely drink without any additional treatment.  The same processes used by a conventional water treatment plant occur naturally in the Edwards.  For more on water quality, filtration, and treatment that occurs within the Aquifer, see the section on water quality. 
What sort of treatment does Edwards water receive before distribution to customers?

None. Well, it receives chlorination, and that's a treatment, but Edwards water does not require the kind of conventional treatment that costs most other cities millions every year. All surface water sources require treatment, as do many other groundwater sources, but Edwards water is drinkable straight from the ground. It wasn't drinkable when it went into the ground, so Aquifer protection is all about protecting the ability of the Edwards to naturally filter and cleanse stormwater runoff, so that we don't have to pay for it.
In Houston, drawing down groundwater supplies caused subsidence of the land surface.  Could that happen here?

The limestones of the Edwards appear to have sufficient bearing capacity so that subsidence will not be a major problem. On the other hand, no one really knows if underground caverns would collapse or if flow patterns would change should the level be drawn lower than ever before.
Will building surface water reservoirs help?

Right now it seems highly unlikely that any more large surface water reservoirs will be built.  Environmental concerns would be many, and landowners would fight tooth and nail against sacrificing their beautiful river valleys to slake San Antonio's thirst.  Reservoirs eventually silt in and have to be replaced, so in terms of a management scheme that will last hundreds and thousands of years, reservoirs have limited value.
Are there any technical solutions to this problem at all?

We probably won't be able to build ourselves a solution with concrete and pipes, at least not a solution that uses Edwards water.  Many of the world's best engineers and planners have been working on this problem for a long time and if there were technical solutions, they probably would have found them by now.  Technology can help a little, but the solution lies in developing effective management institutions and changing cultural attitudes toward the value and use of water.  There is certainly much potential for using traditional technologies like pipes and treatment facilities to bring in new water from elsewhere, but that's different than using technology to augment or manage Edwards water.  The basic issue is we are already using all the water the Aquifer can make available and there is only limited potential for making it yield any additional water on a sustainable basis.
We must be able to build SOMEthing that will help!  What can we do?

Regarding traditional structural projects like dams and pipes, one helpful thing we can do will be to build a system for moving recycled water to people who can use it.   Farmers and miners in the area use drinkable water from the Edwards to grow crops and produce rock products, and these are ideal uses for recycled water.  In the long run it may be necessary to build some small reservoirs for storing recycled water.   For more on this topic, see the sections on water recycling and using recycled water.
What about clearing cedar in the Hill Country to create more recharge?  Will that help?

This one deserves its own section!  See Brush Management in the Edwards Alternatives section. 
 
On the news they always report the Aquifer level in feet above mean sea level.  Does this measure how far down it is until you hit water at the water table?

No.  Generally, confined aquifers do not have water tables.  The Edwards limestone is confined between two relatively impermeable formations and is always saturated; the only place where a water table exists is near the recharge zone where there are no overlying layers (see graphic in Intro Section).  The "Aquifer level" reported on the news has nothing to do with how far down it is until you hit water in the main body of the Aquifer.  It is a measure of how much pressure is being exerted on water in the formation at the location of the test well.  When recharge enters the Aquifer, its weight exerts pressure on water already inside.  This pressure forces water up through openings such as springs and wells.  The "Aquifer level" indicates the top of the water surface in the test well, which is hundreds of feet above the actual Edwards limestone.  A good "indicator well" is one that never becomes artesian...water is never forced so high that it flows out without pumping.  See the section on the J-17 index well for a graphic that illustrates what the Aquifer level means.
People say we need to keep Comal and San Marcos Springs flowing because of endangered species.  Why didn't the endangered fountain darter become extinct the last time Comal Springs went dry during the 1950's drought?

The Comal River population of the fountain darter was completely eliminated by the 1950's drought when the river was reduced to isolated pools of water.  The species was reintroduced using individuals from another population in San Marcos, where the Springs never dried up completely.
If lots of water goes into the Aquifer when it rains, why do we still have floods?

Water enters the Aquifer easily in the recharge zone, but the subsurface drainage is generally inadequate to hold all the water that falls in large rain events.  Recharge conduits and sinkholes quickly become filled and the remaining water has to flow over the surface.  Flash floods are the result.
How did the Edwards Aquifer get its name?

This seems like a question that would have a straightforward answer, but the answer is not simple and it involves a mystery!

The credit for naming the Aquifer goes to the first people who accurately described the Edwards and how it works, even though they never used the word "aquifer".  They were two geologists, R.T. Hill and T. W. Vaughan, who wrote an 1898 report entitled:

The Geology of the Edwards Plateau and Rio Grande Plain adjacent to Austin and San Antonio, Texas, with references to the occurrence of underground waters.  US Geological Survey 18th Annual Report, pt. 2-B, p. 103-321.

In this report, the authors gave the limestone that makes up the Aquifer the name "Edwards".  It had previously been known as Caprina limestone.  That name was abandoned because it is a paleontologic term and geologists prefer that rock formations have geographic names.  The geographic area in the vicinity of the groundwater that Hill & Vaughan were describing was the Edwards Plateau, so they substituted the geographic name Edwards for Caprina.  The Edwards Plateau was named after Edwards county, which was organized and named in 1883.  And Edwards county was named for Hayden Edwards, who lived in Nacogdoches in east Texas.  So far, historians have not been able to explain why Edwards county was named for someone who lived so far away, but a few are trying to unravel the puzzle.

 Although Hill & Vaughan never actually called it an 'aquifer', they referred to the Edwards as an artesian groundwater system, accurately described the catchment and transmission of water in the system, and recognized its large extent from Brackettville to Austin.  They even accurately predicted the existence of the large contiguous artesian zone between San Antonio and Del Rio in which a good water can be obtained anywhere.  Before their publication, the widely held belief was that waters supplying the artesian wells and spring rivers came from the distant Rocky Mountains.  They recognized that was impossible, and explained the true source is the rainfall of the Edwards Plateau.  

Gregg, why did you do this web page?

I got interested in the Edwards Aquifer shortly after I came to San Antonio in 1972.  I started collecting reports and photographs and reading all I could about it, and I always assumed I would write a book.  During those years when I was collecting a lot of material, I was also sort of a computer geek.  When the web was invented in the early 90's, that was about the same time that all the Edwards issues were really coming to a head.  I decided I wanted to learn this new web programming language and started fooling with html tags using a text editor.  Meanwhile, since the Edwards was becoming such a hot issue, I knew there was going to be a real need for untechnical, unbiased information, so that the public could make informed decisions and choices.  A that time, I was doing consulting work for many of the regional water agencies, and I knew none of them had the resources or wherewithal to put anything online.  And even if they did, I knew it would have your typical institutional bias, and that sort of information doesn't always necessarily serve the public very well. So I decided I would put my burgeoning webmaster skills together with all my Edwards resource material and hack together a web page.  The first version went online in early 1995.  Part of keeping the material unbiased and unslanted has meant not accepting sponsorships or advertising.  I don't get anything from webmastering these pages except the satisfaction of knowing they are widely regarded by educators, students, and interested citizens as a reliable, unbiased resource.  About 30,000 people visit this site each month, each one viewing an average of about 12 pages.