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Does San Antonio Have Hard Water?

By Marcus Webb, CWS| Updated October 2026

Short answer: yes, very hard. San Antonio Water System (SAWS) says "the typical hardness in the water provided by SAWS ranges from 15 to 20 gpg (grains per gallon)" (SAWS). That is about 257 to 342 mg/L, well above the 180 mg/L USGS threshold for "very hard." SAWS explains that the calcium carbonate in water from the Edwards and Trinity aquifers is naturally occurring, and that hard water is not a health hazard. SAWS disinfects with free chlorine.

Kitchen faucet with mineral spots, with close-ups of a cloudy glass, a scaled pot and spotty dishes — Illustration: common signs of hard water in a kitchen: spotty fixtures, cloudy glasses, scaled pots and dishes.

San Antonio Hardness in Context

Measure	San Antonio (SAWS)
Typical hardness (SAWS)	15 to 20 grains per gallon
Same range in mg/L (ppm)	About 257 to 342 mg/L as CaCO₃
USGS class	Very hard (over 180 mg/L)
Grains per gallon chart	Very hard (over 10.5 gpg)
Disinfectant	Free chlorine (2025 average 1.46 ppm)

Hardness range from the SAWS water quality FAQ; mg/L calculated at 17.1 mg/L per grain. Disinfectant from the SAWS water quality report. Classes from USGS.

For comparison, that is roughly twice the Houston Main System average of 7.9 gpg and comparable to the top of Phoenix's reported range of 10 to 17.6 gpg. San Antonio sits among the hardest large-city water supplies we cover; see our city guides and hardness scale.

Where San Antonio Water Comes From

The SAWS water quality report says its source water "originates as groundwater from the Edwards, Carrizo, Simsboro, Trinity and Wilcox aquifers," with surface water from Canyon Lake in some areas. SAWS also buys water from six suppliers: Canyon Regional Water Authority, GBRA Western Canyon Water Supply, Oliver Ranch, Schertz Seguin Local Government Corporation, Texas Water Supply Co. and Vista Ridge LLC.

The Edwards Aquifer is limestone, which is mostly calcium carbonate, so water that passes through it picks up a lot of hardness. Because SAWS blends several aquifers and purchased supplies, the exact hardness at your tap can differ by neighborhood. SAWS gives a typical range rather than a single number, so test your own tap: test strips for a quick check, or a Hach 5-B titration kit if you are sizing a softener. Our testing guide explains how.

What the Annual Report Shows (and Leaves Out)

The SAWS annual water quality report focuses on regulated contaminants. It notes that secondary constituents such as hardness "are not required to be reported in this document" and points readers to the state's drinking water database. Key figures it does list (SAWS report):

Free chlorine residual (2025): average 1.46 ppm, range 0.16 to 3.7 ppm, under the 4 ppm limit.
Lead (2024 sampling): 90th percentile 1.6 ppb, with no sites over the 15 ppb action level.
Copper (2024 sampling): 90th percentile 0.187 ppm, no sites over the 1.3 ppm action level.
Fluoride (2025): 0.69 ppm, below the 4 ppm limit.

Because SAWS uses free chlorine rather than chloramine, shower filters certified to NSF/ANSI 177 for chlorine reduction are a reasonable match if chlorine smell or dryness bothers you; see best shower filters. Remember that shower filters do not soften water. Older reports are on the SAWS report archive; SAWS also publishes separate reports for some smaller systems it operates.

What 15 to 20 gpg Does at Home

Very hard water shows up quickly. SAWS's own troubleshooting guide lists white or light-colored sediment from hard water, explaining that "calcium carbonate will precipitate when heated or frozen," and recommends that customers "flush hot water heater regularly, 2-3 times a year to remove loose calcium carbonate" (SAWS). That is more often than the once-a-year draining NYSERDA recommends as a general rule. See hard water and water heaters.

Expect heavy scale on faucets and shower heads, spotty dishes, soap scum on glass, crusty kettles, and for many people drier skin and duller hair. Our limescale guide, skin guide and hair guide cover each.

Sizing a Softener for San Antonio

At 15 to 20 gpg, a water softener is the most effective fix for homeowners, and size matters more than in moderate-hardness cities. Using EPA's estimate that a typical family uses about 300 gallons a day:

Hardness	Grains Removed per Day (300 gal)	32,000-grain unit	48,000-grain unit
15 gpg	4,500	About every 6 days	About every 9 days
17.5 gpg	5,250	About every 5 days	About every 8 days
20 gpg	6,000	About every 4 to 5 days	About every 7 days

Our calculation at rated capacity with a 15% reserve. Real capacity depends on the salt setting; see the sizing table in our Fleck review.

Larger families or homes at the top of the range should look at 48,000 grains or more, such as a 48,000-grain Fleck 5600SXT system. The SpringWell SS1 (32,000 grains) suits smaller households at the lower end of the range. Very hard water also means more salt: see our cost guide for salt use at 15 to 20 gpg, and our store-brand comparison for each model's maximum hardness rating. Softening adds sodium in proportion to hardness, about 8 mg/L per grain, so at 17.5 gpg about 140 mg/L; see is softened water safe to drink?

Renters, Drinking Water and Tankless Heaters

Renters: use a chelating shampoo for hair, descale fixtures monthly, and ask your landlord about a softener. See our portable softener guide for RV and camping use.
Drinking water: hard water is safe to drink (SAWS says it is not a health hazard). For taste, or to remove sodium from softened water, an under sink reverse osmosis system works well; protect it with softened feed water, since countertop RO such as AquaTru is not recommended above 10 gpg without softening.
Tankless water heaters: San Antonio's typical range is well above Rinnai's 200 mg/L guideline. Treat the water and flush regularly; see tankless scale prevention.