San Antonio’s First Source

The Edwards Aquifer is a massive underground reservoir and the source for about half of the volume distributed to SAWS customers. The Edwards Aquifer is made up of intensely faulted and fractured carbonate limestone. The dynamics and size of this geologic anomaly make it one of the most productive aquifers in the nation through its storage capacity, flow characteristics, water producing capabilities, and efficient recharging ability.


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edwards inforgraphic

Edwards Aquifer Management

Fountain Darter

In 2023, approximately 49% (~163,000 AF) of water used by SAWS customers came from the Edwards Aquifer. The Edwards Aquifer Authority (EAA) issued water rights through an established permitting process, and today, SAWS goal is to maintain approximately 281,000 AFY of those rights.

Access to these permitted groundwater withdrawal rights is subject to varying levels of availability depending on critical period reductions due to variable weather conditions. These cutbacks in any given year may range from zero percent to 44 percent. In addition to the regulatory cutbacks, SAWS has agreed to reduce pumping by up to 46,300 AF during any single year during a worst-case drought scenario for the benefit of the Edwards Aquifer Habitat Conservation Plan (EAHCP). Therefore, SAWS assumes a firm yield* of approximately 105,000 AFY during worst-case drought conditions. For that reason, SAWS diversified our water supply to ensure our customers water future.


edwards map


Aquifer Storage and Recovery

The H2Oaks Center uses Aquifer Storage & Recovery to store excess Edwards Aquifer drinking water during rainy times in a large-scale, underground reservoir.


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Firm yield – The volume of water which can be produced from a defined source during a repeat of the drought of record under existing regulatory, legal, contractual, hydrological or infrastructure constraints.

AFY – 1 acre-foot per year = 325,851 gallons per year