How hard is the water in Eureka, MO?

Tap water hardness
79mg/L
4.6gpg
Moderately hardReports range 79–164

Reported by Mo American Eureka · June 2025

MO typical
121 mg/L
EPA health violations since 2016
0
Softener for 3 people
24k grain
Data
Utility report

The water in Eureka carries roughly 79 mg/L of dissolved calcium and magnesium, or 4.6 grains per gallon. That is moderately hard water. The number comes from Mo American Eureka, dated June 2025. Reports for this system disagree, with values from 79 to 164 mg/L.

Eureka on the hardness scale, with nearby cities
060120180240300360+MO typical 121Murphy: 104 mg/LMurphy 104Cottleville: 120 mg/LCottleville 120Chesterfield: 121 mg/LChesterfield 121Kirkwood: 130 mg/LKirkwood 130Ladue: 155 mg/LLadue 155Pacific: 197 mg/LPacific 197Arnold: 212 mg/LArnold 212Town and Country: 234 mg/LTown and Country 234Ballwin: 242 mg/LBallwin 242Des Peres: 263 mg/LDes Peres 263Eureka 79mg/L as calcium carbonate060120180240300360+MO 121Murphy: 104 mg/LMurphy 104Chesterfield: 121 mg/LChesterfie. 121Pacific: 197 mg/LPacific 197Town and Country: 234 mg/LTown and C. 234Ballwin: 242 mg/LBallwin 242Des Peres: 263 mg/LDes Peres 26379 mg/Lmg/L as calcium carbonate
Soft 0–60 mg/LModerately hard 61–120 mg/LHard 121–180 mg/LVery hard 181+ mg/L

At 79 mg/L, Eureka is 42 mg/L below the typical Missouri figure of 121. None of the 10 nearest cities we track has softer water. The range nearby runs from 104 mg/L in Murphy to 263 in Des Peres.

What 79 mg/L means at home

You may see faint white spots on glasses and shower doors after the water dries.

Scale builds up slowly. A kettle or coffee maker needs descaling now and then, maybe every few months.

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

Optional. Plenty of households at this level live with it and descale the kettle now and then.

Water softener

Worth a look if spots on glass bother you, or if your tankless water heater manual asks for softer water.

Carbon filter

Improves taste and removes chlorine. It leaves calcium and magnesium in place.

Softener size for Eureka

3 people × 75 gallons a day × 4.6 gpg = 1,037 grains a day. A 24,000-grain unit regenerates about every 23 days.

Size it for your household

EPA record for Eureka's water system

Mo American Eureka · PWSID MO6010258

No health-based violations since 2016

Serves about 11,000 people from groundwater. EPA lists this system as inactive.

Health-based
0
Monitoring or reporting
0
Open now
0

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 Eureka water hard?

Somewhat. It measures about 79 mg/L (4.6 grains per gallon), which the USGS classes as moderately hard.

What is the water hardness in Eureka in grains per gallon?

About 4.6 gpg. One grain per gallon equals 17.1 mg/L, so 79 mg/L divided by 17.1 gives 4.6.

What size water softener do I need in Eureka?

For 3 people using 75 gallons each per day, 4.6 gpg works out to about 1,037 grains a day. A 24,000-grain softener covers that with a regeneration about every 23 days.

Has the Eureka water system had EPA violations?

EPA records show no health-based violations for Mo American Eureka since 2016.

Nearby cities

All 90 cities in Missouri

Hardness data: TapWaterData US Water Hardness (utility report, June 15, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.