Hard water in Cape Girardeau, MO
Calculated from the utility's calcium and magnesium results · September 2025
- MO typical
- 121 mg/L
- EPA health violations since 2016
- 1
- Softener for 3 people
- 24k grain
- Data
- Calculated from utility data
Cape Girardeau water measures 237 mg/L (13.9 gpg) of hardness, very hard by USGS standards. TapWaterData worked it out from the calcium and magnesium levels the local utility reports (September 2025).
Cape Girardeau sits 116 mg/L above the typical Missouri figure of 121. Of the 10 nearest cities we track, 4 have softer water and 6 have harder. The range nearby runs from 21 mg/L in Caruthersville to 565 in Park Hills.
What 237 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 237 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 × 13.9 gpg = 3,123 grains a day. A 24,000-grain unit regenerates about every 7 days.
EPA record for Cape Girardeau's water system
1 health-based violation since 2016
Serves about 39,941 people from groundwater.
- Health-based
- 1
- Monitoring or reporting
- 5
- Open now
- 0
EPA lists this system as serving Cape Girardeau.
| Contaminant or rule | Violations | Period | Status |
|---|---|---|---|
| Groundwater Ruletreatment of well water | 1 | 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 Cape Girardeau water hard?
Yes. It measures about 237 mg/L (13.9 grains per gallon), which the USGS classes as very hard.
What is the water hardness in Cape Girardeau in grains per gallon?
About 13.9 gpg. One grain per gallon equals 17.1 mg/L, so 237 mg/L divided by 17.1 gives 13.9.
What size water softener do I need in Cape Girardeau?
For 3 people using 75 gallons each per day, 13.9 gpg works out to about 3,123 grains a day. A 24,000-grain softener covers that with a regeneration about every 7 days.
Has the Cape Girardeau water system had EPA violations?
EPA records show 1 health-based violation for Cape Girardeau PWS since 2016, involving Groundwater Rule. There were also 5 monitoring or reporting violations, which are about late or missing tests and notices.
Nearby cities
- Jackson268 mg/LVery hard
- Sikeston163 mg/LHard
- Farmington276 mg/LVery hard
- Poplar Bluff165 mg/LHard
- Park Hills565 mg/LVery hard
- Bonne Terre339 mg/LVery hard
- Caruthersville21 mg/LSoft
- Festus247 mg/LVery hard
- Kennett57 mg/LSoft
- De Soto312 mg/LVery hard
Hardness data: TapWaterData US Water Hardness (calculated from utility data, September 26, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.