San Antonio, TX water hardness: 15–20 grains per gallon (about 257–342 mg/L)
San Antonio Water System (SAWS) says “the typical hardness in the water provided by SAWS ranges from 15 to 20 gpg.” That is very hard on the USGS scale.
Why this page uses the FAQ, not the annual report
We read the 2026 SAWS Main System Water Quality Report (PDF), which uses 2025 data. It has no hardness figure. It says secondary constituents such as calcium “are not required to be reported in this document” and points to the state's Texas Drinking Water Watch database. We could not reach that database on 2026-10-26 (the service was unavailable). So the only SAWS-published hardness figure we found is the FAQ range above.
| Figure | gpg | mg/L (ppm) | Whose number |
|---|---|---|---|
| Low end of typical range | 15 | 256.5 | gpg from SAWS; mg/L our conversion |
| High end of typical range | 20 | 342 | gpg from SAWS; mg/L our conversion |
Where San Antonio's water comes from
The 2026 report lists groundwater from the Edwards, Carrizo, Simsboro, Trinity and Wilcox aquifers, and, in some areas, surface water from Canyon Lake. SAWS also buys water from Canyon Regional Water Authority, GBRA Western Canyon, Oliver Ranch, Schertz-Seguin Local Government Corporation, Texas Water Supply Co. and Vista Ridge LLC. The FAQ says the calcium carbonate in Edwards and Trinity water is naturally occurring.
Hardness by aquifer or neighborhood: not published. SAWS does not give hardness per source, so we cannot tell you whether your area gets harder or softer water. Your bill and the report archive show which SAWS system serves you. SAWS also runs smaller systems (Castle Hills, Geronimo Forest, Mountain Laurel, Northeast, Texas Research Park); on 2026-10-26 the archive listed only the Main System report for 2026.
What 15–20 gpg means at home
Water softener
Without a test, program a softener at 20 gpg, the top of SAWS's range. If you test your tap, use that number. Very hard water uses up softener capacity fast, so a softener sized for softer water will regenerate often. Check the sizing against 20 gpg and your household's daily water use.
Dishwasher
Use the highest or second-highest hardness level in your manual (15–20 gpg is about 14–19 °dH). Keep rinse aid filled, and keep the salt reservoir filled if your model has one. White film on glasses is the usual sign the setting is too low.
Kettles, coffee makers, water heaters and fixtures
At this hardness, scale builds quickly on anything that heats water. Descale kettles and coffee makers often, and follow the water heater maker's flushing advice. SAWS states that hard water “is not a health hazard.”
Disclosure: this page may later carry affiliate links. No affiliate links are live today. If we add one, it will be marked and explained on our disclosure page. Product links never change the hardness numbers.
Sources
- SAWS, Water Quality FAQs, “What is hardness?”: https://www.saws.org/your-water/water-quality/saws-water-quality-concerns/faqs/
- SAWS, 2026 Main System Water Quality Report (PDF, 2025 data; no hardness figure): https://www.saws.org/wp-content/uploads/2026/05/2026-SAWS-Water-Quality-Report.pdf
- SAWS, 2026 Main System Water Quality Report (web version): https://www.saws.org/your-water/water-quality/water-quality-report/water-quality-report-san-antonio-water-system/
- SAWS, Water Quality Report archive (all systems): https://www.saws.org/your-water/water-quality/download-water-quality-reports/
- USGS Water Science School, Hardness of Water: https://www.usgs.gov/water-science-school/science/hardness-water