Hard water in San Marcos, TX
Reported by City of San Marcos · February 2025
- TX typical
- 112 mg/L
- EPA health violations since 2016
- 2
- Softener for 3 people
- 24k grain
- Data
- Utility report
The water in San Marcos carries roughly 212 mg/L of dissolved calcium and magnesium, or 12.4 grains per gallon. That is very hard water. The number comes from City of San Marcos, dated February 2025. Reports for this system disagree, with values from 212 to 277 mg/L.
San Marcos sits 100 mg/L above the typical Texas figure of 112. None of the 10 nearest cities we track has harder water. The range nearby runs from 63 mg/L in Shady Hollow to 202 in New Braunfels.
What 212 mg/L means at home
Scale forms fast here. Kettles and coffee makers need regular descaling, and showerheads clog unless you clean them.
Tank water heaters collect mineral sediment that insulates the water from the burner, so flushing the tank matters more than usual.
Dishes and glass shower doors spot easily. Soap scum and a dull film on hair or laundry are common complaints.
Hardness is not a health problem, and EPA sets no limit for it. It is a matter of scale and soap.
What to do about it
At 212 mg/L most of the trouble is scale, and only a few things deal with it.
Ion-exchange water softener
The standard whole-house fix. It swaps calcium and magnesium for sodium or potassium and needs salt plus a drain. Size it with the calculator below.
Salt-free conditioner
No salt and no drain line. It changes how minerals form scale instead of removing them, so water still tests hard.
Reverse osmosis or carbon filter
Under-sink reverse osmosis removes minerals from drinking water only. Plain carbon filters improve taste but do not soften.
3 people × 75 gallons a day × 12.4 gpg = 2,794 grains a day. A 24,000-grain unit regenerates about every 8 days.
EPA record for San Marcos's water system
2 health-based violations since 2016
Serves about 72,970 people from surface water.
- Health-based
- 2
- Monitoring or reporting
- 2
- Open now
- 0
| Contaminant or rule | Violations | Period | Status |
|---|---|---|---|
| Total trihalomethanes (TTHM)a disinfection byproduct | 2 | 2016–2025 | Resolved |
Health-based means a contaminant above its legal limit or a missed treatment step. Monitoring and reporting violations are late or missing tests and notices. Source: EPA ECHO, 2026Q3 export, violations with periods starting 2016 or later. Full EPA record.
Questions
Is San Marcos water hard?
Yes. It measures about 212 mg/L (12.4 grains per gallon), which the USGS classes as very hard.
What is the water hardness in San Marcos in grains per gallon?
About 12.4 gpg. One grain per gallon equals 17.1 mg/L, so 212 mg/L divided by 17.1 gives 12.4.
What size water softener do I need in San Marcos?
For 3 people using 75 gallons each per day, 12.4 gpg works out to about 2,794 grains a day. A 24,000-grain softener covers that with a regeneration about every 8 days.
Has the San Marcos water system had EPA violations?
EPA records show 2 health-based violations for City of San Marcos since 2016, involving Total trihalomethanes (TTHM). There were also 2 monitoring or reporting violations, which are about late or missing tests and notices.
Nearby cities
- Kyle113 mg/LModerately hard
- Buda136 mg/LHard
- New Braunfels202 mg/LVery hard
- Seguin125 mg/LHard
- Shady Hollow63 mg/LModerately hard
- Belterra143 mg/LHard
- Dripping Springs148 mg/LHard
- Cibolo85 mg/LModerately hard
- Schertz176 mg/LHard
- Bee Cave110 mg/LModerately hard
Hardness data: TapWaterData US Water Hardness (utility report, February 27, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.