Water Banking for Environmental Protection

The Edwards aquifer is the primary source of drinking water for the City of San Antonio, the seventh largest city in the country. Withdrawals are regulated by the Edwards Aquifer Authority and permits can be curtailed during drought to ensure adequate supplies and maintain flows in San Marcos and Comal Springs, home to several endangered species. Despite an over 30 percent reduction in per capita consumption since the mid-1980’s, development of alternative sources of potable water supplies and storage strategies was necessary to ensure protection of the environment and continued economic prosperity of the region, especially during drought.

One of the more innovative strategies implemented by San Antonio Water System (SAWS) involves managing their Edwards withdrawals to achieve full permit utilization while minimizing regional impact on spring flows and aquifer levels that trigger permit reductions. During seasonal periods of high spring flows and water levels, the Edwards aquifer is pumped to meet both customer water demand and to provide water for storage. The surplus is stored in the Carrizo sand formation in southern Bexar County and recovered to augment supplies during extended drought periods.

The system has been used twice by SAWS to reduce pumping pressure on the Edwards aquifer; once in 2006 and a second time beginning in 2011. In 2006, approximately 4,900 acre-feet of stored Edwards water was recovered over five months, at a maximum rate of nearly 40 mgd. Recovery in the more severe drought, which began in October of 2010, was initiated in April 2011. Through August 2011, 10,072 acre-feet of stored Edwards water was recovered at a peak rate of 40 mgd. Without the ASR project, it is widely accepted that more restrictive stages of drought reductions might have occurred with associated lower rates of spring flows and water levels.