Hard water in Stillwater, OK
County estimate from 743 water samples in Payne County · July 2026
- OK typical
- 152 mg/L
- EPA health violations since 2016
- 16
- Softener for 3 people
- 24k grain
- Data
- County estimate
Water samples from around Stillwater put hardness at about 236 mg/L (13.8 gpg), which would be very hard on the USGS scale. Treat this as a rough guide: it is the median of 743 samples taken across Payne County, mostly wells and streams, not a test of Stillwater's treated tap water. One more reason for caution: EPA lists Stillwater's water system as using surface water, which is often softer than the wells behind the county figure.
Stillwater sits 84 mg/L above the typical Oklahoma figure of 152. Of the 10 nearest cities we track, 8 have softer water and 2 have harder. The range nearby runs from 111 mg/L in Sand Springs to 422 in Ponca City.
What 236 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 236 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 × 13.8 gpg = 3,110 grains a day. A 24,000-grain unit regenerates about every 7 days.
EPA record for Stillwater's water system
16 health-based violations since 2016
Serves about 53,000 people from surface water.
- Health-based
- 16
- Monitoring or reporting
- 5
- Open now
- 0
EPA lists this system as serving Stillwater.
| Contaminant or rule | Violations | Period | Status |
|---|---|---|---|
| Surface Water Treatment Rulefiltration and disinfection | 8 | 2016–2023 | Resolved |
| Total organic carbon removaltreatment requirement | 8 | 2016–2022 | 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 Stillwater water hard?
Yes. It measures about 236 mg/L (13.8 grains per gallon), which the USGS classes as very hard.
What is the water hardness in Stillwater in grains per gallon?
About 13.8 gpg. One grain per gallon equals 17.1 mg/L, so 236 mg/L divided by 17.1 gives 13.8.
What size water softener do I need in Stillwater?
For 3 people using 75 gallons each per day, 13.8 gpg works out to about 3,110 grains a day. A 24,000-grain softener covers that with a regeneration about every 7 days.
Has the Stillwater water system had EPA violations?
EPA records show 16 health-based violations for Stillwater Utilities Authority since 2016, involving Surface Water Treatment Rule, Total organic carbon removal. There were also 5 monitoring or reporting violations, which are about late or missing tests and notices.
Nearby cities
- Edmond135 mg/LHard
- Ponca City422 mg/LVery hard
- The Village134 mg/LHard
- Enid400 mg/LVery hard
- Piedmont123 mg/LHard
- Oklahoma City157 mg/LHard
- Sand Springs111 mg/LModerately hard
- Shawnee140 mg/LHard
- Bethany221 mg/LVery hard
- Sapulpa111 mg/LModerately hard
Hardness data: TapWaterData US Water Hardness (county estimate, July 4, 2026), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.