Hard water in St. Peters, MO
Calculated from the utility's calcium and magnesium results · June 2024
- MO typical
- 121 mg/L
- EPA health violations since 2016
- 0
- Softener for 3 people
- 24k grain
- Data
- Calculated from utility data
St. Peters water measures 168 mg/L (9.8 gpg) of hardness, hard by USGS standards. TapWaterData worked it out from the calcium and magnesium levels the local utility reports (June 2024).
At 168 mg/L, St. Peters is 47 mg/L above the typical Missouri figure of 121. Of the 10 nearest cities we track, 7 have softer water and 3 have harder. The range nearby runs from 79 mg/L in Eureka to 263 in Des Peres.
What 168 mg/L means at home
Expect white crust on faucets and showerheads, plus spots on dishes that come out of the dishwasher.
Kettles collect scale quickly. Water heaters build up sediment at the bottom of the tank, which makes them work harder over time.
Soap and detergent need a little more to lather, and soap scum shows up in the tub.
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 168 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 × 9.8 gpg = 2,210 grains a day. A 24,000-grain unit regenerates about every 10 days.
EPA record for St. Peters's water system
No health-based violations since 2016
Serves about 52,575 people from surface water.
- Health-based
- 0
- Monitoring or reporting
- 1
- Open now
- 0
EPA lists this system as serving St. Peters.
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 St. Peters water hard?
Yes. It measures about 168 mg/L (9.8 grains per gallon), which the USGS classes as hard.
What is the water hardness in St. Peters in grains per gallon?
About 9.8 gpg. One grain per gallon equals 17.1 mg/L, so 168 mg/L divided by 17.1 gives 9.8.
What size water softener do I need in St. Peters?
For 3 people using 75 gallons each per day, 9.8 gpg works out to about 2,210 grains a day. A 24,000-grain softener covers that with a regeneration about every 10 days.
Has the St. Peters water system had EPA violations?
EPA records show no health-based violations for ST Peters PWS since 2016. There were also 1 monitoring or reporting violation, which are about late or missing tests and notices.
Nearby cities
- Cottleville120 mg/LHard
- Maryland Heights121 mg/LHard
- Chesterfield121 mg/LHard
- Lake St. Louis123 mg/LHard
- Town and Country234 mg/LVery hard
- Ballwin242 mg/LVery hard
- Des Peres263 mg/LVery hard
- Ladue155 mg/LHard
- Kirkwood130 mg/LHard
- Eureka79 mg/LModerately hard
Hardness data: TapWaterData US Water Hardness (calculated from utility data, June 16, 2024), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.