DYK: San Antonio sits on top of one of the largest water reservoirs of its kind anywhere in the U.S.

Brought to you by the SA300 Committee

SAN ANTONIO – Did you know that San Antonio sits on top of one of the largest water reservoirs of its kind anywhere in the U.S.?

The Edwards Aquifer provides San Antonio with an abundant source of groundwater vital to the livelihood of a growing population and an expanding economy.


The Name:

In the US Geological Survey 18th annual report, authors R.T. Hill and T.W. Vaughan named the Edwards plateau after Edwards county, which was organized and appointed in 1883.

Edwards County was named for Hayden Edwards, one of the original settlers in Nacogdoches in East Texas.

The word aquifer means a body of permeable rock that can contain or transmit groundwater.

Put It together - We get The Edwards Aquifer.


It’s Origins:

About 100,000,000 years ago, Texas was covered by a shallow sea that was habitat for prehistoric marine animals.

When the sea creatures died, their remains—skeletons and shells made of calcium carbonate—were deposited on the seafloor.

The calcium carbonate and other minerals from seawater formed layers, or strata, on the seafloor. After a while, these layered deposits compacted into limestone, known today as the Edwards and associated limestones.

The Edwards Aquifer has been a source of water for people in south central Texas for more than 12,000 years.

Today, it is the primary source of water for approximately 2 million people.


How it Works:

About 17 million years ago, a shift in the earth’s crust caused central Texas to be lifted above the level of the sea.

As the ground rose, the limestone broke, producing fractures and faults. The result was a stair-step landscape that is now referred to as the Balcones fault zone.

Rainfall enters the aquifer through fractures, caves, sinkholes and other features and replenishes the aquifer.

The sheer weight of new water entering the aquifer puts tremendous pressure on the water that is already deeper down in the formation.

Flowing wells and springs exist where hydraulic pressure is sufficient to force water up through wells and faults to the surface.


How Much Water is in the Aquifer:

A measure of the percentage of pore spaces within the rock that are connected to other pore spaces, known as effective porosity, gives a  reasonable estimate of a staggering 25-55 million acre-feet of water currently residing in the Edwards Aquifer.

One acre-foot equals 43,560 cubic feet and is equivalent to 325,851 gallons.

325,851 x 30,000,000 = 977,553,000,000 gallons of water.


Here are links to web resources about the Edwards aquifer and its impact on the Texas community.



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