San Antonio Water Hardness & Quality Report (2026)

San Antonio's water is managed by San Antonio Water System (SAWS), drawing from two primary sources. The dominant supply is the Edwards Aquifer — a vast karst limestone reservoir underlying the Hill Country and San Antonio region — which provides groundwater through a network of SAWS production wells. Surface water is supplemented from the Canyon Lake Reservoir on the Guadalupe River and the Guadalupe-Blanco River Authority (GBRA) pipeline system. SAWS also operates the H2Oaks Center aquifer storage and recovery facility, injecting treated surface water during wet seasons for later extraction during drought periods. The mixed source designation reflects this blending of hard Edwards Aquifer groundwater with treated surface reservoir supply.

San Antonio's very high hardness of 399 mg/L is primarily driven by the Edwards Aquifer's extraordinary mineral content. The aquifer is carved into Lower Cretaceous (Aptian–Albian) Edwards Limestone and Georgetown Formation — shallow marine carbonate rock deposited 95–115 million years ago in a warm, clear tropical sea that covered central Texas. Rainwater infiltrating the karst dissolves calcium carbonate and dolomite at very high rates through solution channels, caves, and fracture networks. Few aquifer systems in North America produce more naturally hard water than the Edwards on a consistent basis.

San Antonio residents experience some of the most pronounced hard-water effects in the country. Thick white calcium carbonate deposits form rapidly on showerheads, faucets, glass shower doors, and appliances. Soap and shampoo lather poorly, and scale significantly shortens the lifespan of water heaters, dishwashers, and washing machines. A whole-house water softener is essentially standard equipment in San Antonio homes, and most appliance retailers in the region implicitly assume softener use. Descale showerheads and aerators monthly for best long-term results.