How Hard Is the Water in San Antonio? Grains Per Gallon Explained

If you moved to San Antonio and immediately noticed white crust on the faucet, soap that will not lather and a dishwasher that leaves everything cloudy, you are not imagining it. Water across most of Bexar County is genuinely hard — commonly in the 15 to 20 grains per gallon range, which the Water Quality Association classifies as very hard.

What grains per gallon actually measures

Hardness is the amount of dissolved calcium and magnesium in your water. It is reported either in grains per gallon (gpg) or in milligrams per liter (mg/L, the same as parts per million). One grain per gallon equals about 17.1 mg/L. So a home at 17 gpg is drinking and bathing in roughly 290 mg/L of dissolved mineral.

• 0–3 gpg: soft
• 3–7 gpg: moderately hard
• 7–10 gpg: hard
• 10+ gpg: very hard — where most of San Antonio sits

Why the Edwards Aquifer makes it this way

San Antonio's drinking water comes largely from the Edwards Aquifer, a limestone formation. Rainwater picks up carbon dioxide, turns mildly acidic, and slowly dissolves calcium carbonate out of that limestone on its way down. The result is water that is clean, well regulated and safe to drink — and loaded with mineral. Hardness is not a contamination problem; it is a geology problem.

What that hardness does inside your house

Dissolved calcium comes out of solution when water is heated or evaporates. That is scale. It plates the inside of your water heater, coats heating elements in the dishwasher, narrows shower heads and leaves the spots you keep wiping off glass.

• Water heaters lose efficiency as scale insulates the element or burner surface
• Soap reacts with calcium instead of lathering, so you use far more of it
• Laundry stiffens and colors dull faster
• Fixtures and glass doors need constant descaling
• Skin and hair feel dry because soap curd does not rinse fully away

How to find your own number

SAWS publishes annual water quality reports with hardness ranges by system, but the number at your tap varies by neighborhood, by well field and by season. Homes on private wells north of Loop 1604 can read very differently from a house inside 410. A test strip gets you close; a titration test at the sink gets you exact.

BlueWell Water Co tests hardness, chlorine and TDS at your kitchen sink for free anywhere in the San Antonio area, then quotes only the equipment your house actually needs.

What to do about it

The only technology that actually removes hardness minerals is ion exchange — a traditional water softener sized to your grain load and household size. Everything else on the market either conditions scale so it sticks less (template assisted crystallization) or treats a different problem entirely, like chlorine taste or sediment.