San Antonio water hardness (SAWS) and choosing a water softener
Last reviewed: October 23, 2026.
If you live in San Antonio, you already know the signs: white crust on faucets, spots on glasses, and a ring in the kettle. San Antonio Water System (SAWS) water is some of the hardest city water in Texas. This guide covers what SAWS publishes about hardness, where the minerals come from, what they mean for water heaters, and how to think about a softener. Every number below links to its source.
How hard is San Antonio water?
SAWS's water quality FAQ says it plainly: "The typical hardness in the water provided by SAWS ranges from 15 to 20 gpg (grains per gallon)." In parts per million, that is roughly 257 to 342 ppm (1 gpg is about 17.1 ppm). The US Geological Survey calls anything over 180 mg/L (ppm) "very hard," so San Antonio sits well inside that band. For comparison with other cities, see our Texas water hardness by city table.
SAWS's annual water quality report (the 2026 report covers 2025 data) doesn't list hardness in its main tables. It notes that secondary constituents are posted on the state's Texas Drinking Water Watch site, under SAWS's public water system ID TX0150018. Our guide on how to read a Texas water quality report walks through it. The same report shows no violations for 2025.
One important point: hardness isn't a safety issue. SAWS's FAQ says "Hard water is not a health hazard," and the US Geological Survey describes hardness as "not a health concern, but it can be a nuisance." A softener is about scale, soap and appliances, not about making the water safe.
Where the hardness comes from: the Edwards Aquifer
SAWS says the calcium carbonate in its water occurs naturally, coming from the Edwards and Trinity Aquifers. The 2026 report lists the system's sources as the Edwards, Carrizo, Simsboro, Trinity and Wilcox aquifers, plus Canyon Lake surface water in some areas. SAWS also buys water from several regional suppliers.
The Edwards is the big one. The Edwards Aquifer Authority describes it as a karst aquifer: limestone that mildly acidic rainwater (carbonic acid) has dissolved over time, leaving channels and caves. About 1,250 square miles of Edwards limestone is exposed at the surface in the Recharge Zone, where rain soaks straight in. Water that moves through limestone picks up calcium carbonate along the way. That is why water from the aquifer is so hard.
Scale, water heaters and tankless heaters
Hard water leaves scale wherever it is heated or evaporates. You see it on fixtures and shower glass. Inside a water heater, you don't see it, and that's where it costs the most.
Tankless heaters are especially sensitive. A US Department of Energy Building America guide on switching to tankless water heaters says scale buildup in the heat exchanger restricts flow and can shorten the unit's life. It says recommended flushing ranges from twice a year to once every three years, depending on the water. It also says: "If the hardness of the supply water exceeds 8 grains per gal (136 ppm) to 14 grains per gal (239 ppm) or higher, manufacturers may require that a water softener be installed." At 15 to 20 gpg, San Antonio water is above that whole range. If you have a tankless heater or plan to add one, read the installation manual's water quality section before you decide on treatment, since warranty terms can depend on it.
Sizing example for a San Antonio household
Softener size comes down to how many grains of hardness you remove each day. The simple version: hardness (gpg) × people × gallons per person per day.
For gallons per person, EPA WaterSense says the average American family uses more than 300 gallons of water a day at home, with about 70% of that used indoors. We use 75 gallons per person per day. That is on the safe side, since outdoor watering usually doesn't run through a softener.
| Household | Hardness | Grains per day | Grains per week |
|---|---|---|---|
| 2 people | 17.5 gpg (SAWS midpoint) | 2,625 | 18,375 |
| 4 people | 17.5 gpg | 5,250 | 36,750 |
| 4 people | 20 gpg (top of SAWS range) | 6,000 | 42,000 |
| 6 people | 20 gpg | 9,000 | 63,000 |
Your target is a softener that can handle about a week of hardness between regenerations at the salt setting you plan to use. A family of four in San Antonio needs roughly 37,000 to 42,000 grains of usable capacity per week. Keep in mind that a unit's advertised capacity is usually measured at its highest salt setting, and efficient settings give less capacity per regeneration. Ask the seller what capacity you get at the salt dose you'll actually use. Plug your own hardness and household size into the same formula. Your hardness may vary by neighborhood depending on which source feeds your area.
Salt-based vs salt-free at 15–20 gpg
Salt-based (ion exchange) softeners actually remove calcium and magnesium, swapping them for sodium or potassium on a resin bed. University of Nebraska Extension's 2025 guide on salt-free options calls ion exchange the common way to remove hardness.
Salt-free conditioners are a different thing. The same Nebraska Extension guide says these devices "do not remove the hardness"; they are descalant devices. The most common type, template-assisted crystallization (TAC), turns hardness minerals into tiny crystals that are less likely to stick, and may need pretreatment if there is iron or manganese. The guide calls magnetic devices "unproven" and notes that "few conclusive studies confirm the efficiency of these devices for residential use."
At San Antonio's hardness, that matters. If you want soft water (less soap, no spots, protection for a tankless heater whose manual calls for softened water), a salt-based softener is the tool that removes hardness. A salt-free unit may reduce scale in pipes, but your water stays just as hard, and it won't meet a "softener required" condition.
What to look for in a softener
- Grain capacity that matches your math. Use the table above. Too small means frequent regenerations and more salt. Far too big can let the resin sit unused.
- A demand-initiated valve. The Building America Solution Center (Pacific Northwest National Laboratory) explains that softeners with demand-initiated regeneration (DIR) use a flow meter or hardness sensor to regenerate only when needed. Older time-clock units regenerate on a schedule, typically every four days to once a week, whether you used the water or not.
- A certified efficiency rating. The same PNNL page says an efficiency rating under NSF/ANSI 44 (Section 7) or WQA S-100 requires DIR, at least 3,350 grains removed per pound of salt, and no more than 5.0 gallons of water per 1,000 grains removed. Look for NSF or WQA Gold Seal certification on the specific model.
- Carbon pre-filtration if taste bothers you. A softener doesn't remove chlorine taste. SAWS adds chlorine as a disinfectant (its FAQ says about 1.0 ppm, and its 2025 report shows a free chlorine residual averaging 1.46 ppm). See our Texas filtration guide for how carbon and reverse osmosis fit with a softener.
If you'd like a worked example of how one brand's models line up with San Antonio's hardness, see our SoftPro water softener guide for Texas, which includes a sizing worksheet.
Discharge notes (septic and city sewer)
Softeners send salty rinse water down the drain when they regenerate. If a home in the San Antonio area is on a septic system, Texas law applies. Texas Health and Safety Code §366.013 says a softener that drains into an on-site sewage system must be designed to conserve water, use a demand-initiated regeneration control, and be labeled. Units installed before September 1, 2003 are grandfathered until they're replaced.
For homes on the SAWS sewer system, we didn't find a SAWS rule that restricts softener discharge. Check with a licensed plumber and the City of San Antonio permit office before installing, since local codes cover drain connections such as air gaps.
Bottom line
San Antonio water typically runs 15 to 20 gpg, which is very hard. If scale, spotting or a tankless heater is your concern, a properly sized, demand-initiated salt-based softener is the option that actually removes hardness. Austin is a useful contrast: its water averages about 5.4 gpg. See do you need a water softener in Austin?
Sources
- San Antonio Water System, Water Quality FAQs (hardness 15–20 gpg; Edwards and Trinity source; chlorine dose)
- San Antonio Water System, 2026 Water Quality Report (2025 data), main system
- Edwards Aquifer Authority, About the Edwards Aquifer
- US Geological Survey, Hardness of Water
- US Department of Energy, Building America, Measure Guideline: Transitioning to a Tankless Water Heater (IBACOS, 2012)
- University of Nebraska–Lincoln Extension, NebGuide G2275: Salt-Free Water "Softener" Options
- Pacific Northwest National Laboratory, Building America Solution Center, Water Softeners
- US EPA WaterSense, How We Use Water
- Texas Health and Safety Code, §366.013, Water Softeners
Information only; not plumbing or health advice. For water quality questions, contact your utility.