Water for the Future

Among the rolling hills of southern Bexar County, San Antonio Water System operates one of the largest reservoirs of its kind anywhere in the U.S. — filled with enough water to supply SAWS’ customers for three-quarters of the year. Never seen it? That’s because it’s all underground!

ASR infographic

The Aquifer Storage and Recovery (ASR) Program is a key component of SAWS’ 2017 Water Management Plan. The first major project funded by SAWS customers through the Water Supply Fee, SAWS opened the ASR in June 2004.


Water rights allocation from the Edwards Aquifer is limited by legislation and Edwards Aquifer Authority rules. During wetter periods, permit allocations were not fully utilized, and the remaining permitted rights were lost at the end of the year. Storing it into the ASR is how SAWS makes the most out of their Edwards Aquifer allocation.

ASR technology is a proven method of storing water underground. The concept is simple. SAWS pumps excess Edwards Aquifer permitted water underground into the Carrizo Aquifer at the H2Oaks facility in south Bexar County. Later, during hot and dry stress periods as well as during extended droughts, the drinking water is pumped back into the distribution system to help meet demand.  Additionally, ASR plays a key role in protecting endangered species at Comal and San Marcos Springs as a major component of the Edwards Aquifer Habitat Conservation Plan. The ability to offset demand from the Edwards Aquifer during extreme drought is key to ensuring survival of those species.

During the record-breaking drought of 2011-2014, SAWS recovered more than 50,000 AF of stored Edwards Aquifer water to distribute to its customers. In 2023, SAWS distributed close to 28,300 AF of stored Edwards water to help meet demand during the driest months of the year, almost double the amount that was distributed the previous year. SAWS was also able to store about 5,600 AF, finishing the year with of total stored volume of about 166,300 AF. SAWS plans for total storage volume of approximately 200,000 AF of Edwards water.

Let Sarah take you on the 90-second tour


SAWS Aquifer Storage & Recovery Explained in 90 Seconds

ASR map



H2Oaks Center

The H2Oaks Center is home to three water supplies, all operated from the H2Oaks control room: desalinated water, aquifer storage and recovery, and local Carrizo Aquifer.


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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

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