San Antonio’s water hardness typically ranges from 15 to 20 grains per gallon, according to the San Antonio Water System (SAWS), or about 257 to 342 mg/L. That’s very hard on the USGS scale, among the hardest big-city supplies in the US. Set a softener to 20 gpg, the top of SAWS’s range, unless a test of your own tap says otherwise.
On this page
15–20 gpg about 257–342 mg/L as CaCO3
SAWS water quality FAQs. Scale: USGS classes up to 300 mg/L; San Antonio runs off the end.
| Typical hardness | 15–20 gpg (SAWS) |
|---|---|
| In mg/L or ppm | about 257–342 (SofterTap conversion) |
| USGS class | Very hard (over 180 mg/L) |
| Suggested softener setting | 20 gpg |
| Main source | Edwards Aquifer, “over half” of the drinking water |
| Other sources | Trinity, Carrizo, Simsboro (Vista Ridge) and Wilcox aquifers, Canyon Lake, recycled water |
| Utility | San Antonio Water System (SAWS) |
Below: why the water is so hard, what the range means in other units, the softener size and salt a San Antonio home needs, and how to deal with the scale if you don’t soften.
Why San Antonio water is so hard
SAWS explains that “as water moves through soil and rock, it dissolves small amounts of minerals that make water hard”, and names the Edwards and Trinity aquifers as the source of the calcium carbonate in its water. The Edwards is a limestone aquifer, and it has always been the city’s backbone: SAWS says it supplied 100% of San Antonio’s water in 1995 and still provides more than half of its drinking water today.
Since then SAWS has added six more sources, including the Carrizo and Simsboro aquifers (the Simsboro supplies about 70% of the Vista Ridge pipeline’s water), a brackish-water desalination plant on the Wilcox aquifer and surface water from Canyon Lake. That’s one reason SAWS gives a range rather than one figure: the mix reaching a given neighbourhood varies.
San Antonio water hardness in other units
| Unit | 15 gpg | 17.5 gpg (midpoint) | 20 gpg |
|---|---|---|---|
| mg/L or ppm as CaCO3 | 257 | 300 | 342 |
| German degrees (°dH) | 14.4 | 16.8 | 19.2 |
| French degrees (°f) | 25.7 | 30.0 | 34.2 |
| Clark degrees (°e) | 18.0 | 21.0 | 24.0 |
| mmol/L | 2.57 | 3.00 | 3.42 |
For a dishwasher with a built-in softener, look up which level covers 19 °dH in your manual’s table; on most machines it’s near the top of the scale.
Setting a water softener in San Antonio
Enter 20. SAWS doesn’t publish a setting, so we suggest the top of its range: a setting a little too high costs some salt, while one too low lets hard water through before each regeneration. Our hardness setting guide shows the trade-off in numbers. A home test strip can narrow it down for your street; take readings in different seasons if you can.
On a private well outside SAWS’s network, test for iron as well. Softener manuals such as Pentair’s add 5 to the setting for each ppm of iron.
Softener size and salt use for San Antonio water
At 20 gpg and 80 gallons per person per day, a San Antonio softener works hard. The last two columns show salt for an efficiency-rated softener (3,350 grains per lb, the NSF/ANSI 44 minimum) at $8.76 per 40 lb bag.
| People | Grains per week | Nominal size | Size at medium salt | Salt per year | Salt cost per year |
|---|---|---|---|---|---|
| 1 | 11,200 | 24,000 | 24,000 | 174 lb | $38 |
| 2 | 22,400 | 24,000 | 32,000 | 349 lb | $76 |
| 3 | 33,600 | 40,000 | 48,000 | 523 lb | $115 |
| 4 | 44,800 | 48,000 | 64,000 | 697 lb | $153 |
| 5 | 56,000 | 64,000 | 80,000 | 872 lb | $191 |
| 6 | 67,200 | 80,000 | over 80,000 | 1,046 lb | $229 |
A family of four goes through about 17 bags of salt a year, or one every three weeks (see how long a bag of salt lasts). At this hardness the salt setting matters a lot: the same family could use about 70% more salt on a softener stuck at its highest dose, as our guide to how much salt a water softener uses shows. Size so the medium setting covers a week, using the calculator below or the full method in what size water softener do I need.
This calculator needs JavaScript. The table above covers 1 to 6 people.
Living with San Antonio water without a softener
SAWS is clear that “hard water is not a health hazard”, and adds that the National Research Council considers hard water a small contributor of calcium and magnesium to the diet. The cost is scale. A family of four on 20 gpg water sends roughly 150 kg (about 330 lb) of dissolved hardness through the house each year, by our calculation, and the part that drops out where water is heated is what coats kettles, water heaters and shower heads.
Without a softener, plan on:
- Descaling the kettle and coffee maker often: monthly is reasonable at this hardness. Here’s how to descale a kettle.
- Soaking shower heads and aerators in vinegar every few months.
- Draining sediment from a tank water heater. The City of Anaheim, which also has mineral-rich water, recommends every six months.
- Setting the dishwasher to its high hardness level and keeping its salt topped up.
Our guide on how to remove limescale gives the method and contact time for each.
Suburbs and other utilities
SAWS is the main utility for San Antonio, but not every address in Bexar County is on its system. Some suburbs and unincorporated areas are served by other utilities or private wells, with their own water and their own reports. Use the hardness figure from whoever sends your water bill, or test. Other cities are compared in water hardness by city.
Frequently asked questions
Is San Antonio water hard?
Very. SAWS gives a typical range of 15 to 20 gpg (about 257 to 342 mg/L), well above the USGS “very hard” line of 180 mg/L.
What should I set my water softener to in San Antonio?
20 gpg, the top of SAWS’s range, unless a test of your tap gives a different number.
Why is San Antonio water so hard?
Most of it comes from the Edwards Aquifer, a limestone formation. SAWS names the Edwards and Trinity aquifers as the source of the calcium carbonate in its water.
Is San Antonio tap water safe to drink?
Hardness isn’t a safety issue: SAWS states that hard water is not a health hazard. For other water quality questions, see SAWS’s annual water quality report.
Is San Antonio water harder than Austin’s?
Much harder. Austin Water’s 2025 average was 5.4 gpg, partly because Austin draws lake water and softens it with lime at the plant.
