Hard water in Monmouth, IL
Calculated from the utility's calcium and magnesium results · May 2022
- IL typical
- 139 mg/L
- EPA health violations since 2016
- 1
- Softener for 3 people
- 24k grain
- Data
- Calculated from utility data
The water in Monmouth carries roughly 175 mg/L of dissolved calcium and magnesium, or 10.2 grains per gallon. That is hard water. TapWaterData worked it out from the calcium and magnesium levels the local utility reports (May 2022).
Monmouth sits 36 mg/L above the typical Illinois figure of 139. Of the 10 nearest cities we track, 2 have softer water and 8 have harder. The range nearby runs from 54 mg/L in Kewanee to 401 in Canton.
What 175 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 175 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 × 10.2 gpg = 2,300 grains a day. A 24,000-grain unit regenerates about every 10 days.
EPA record for Monmouth's water system
1 health-based violation since 2016
Serves about 8,902 people from groundwater.
- Health-based
- 1
- Monitoring or reporting
- 1
- Open now
- 0
EPA lists this system as serving Monmouth.
| Contaminant or rule | Violations | Period | Status |
|---|---|---|---|
| Combined radiumnaturally occurring radioactivity | 1 | 2024 | 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 Monmouth water hard?
Yes. It measures about 175 mg/L (10.2 grains per gallon), which the USGS classes as hard.
What is the water hardness in Monmouth in grains per gallon?
About 10.2 gpg. One grain per gallon equals 17.1 mg/L, so 175 mg/L divided by 17.1 gives 10.2.
What size water softener do I need in Monmouth?
For 3 people using 75 gallons each per day, 10.2 gpg works out to about 2,300 grains a day. A 24,000-grain softener covers that with a regeneration about every 10 days.
Has the Monmouth water system had EPA violations?
EPA records show 1 health-based violation for Monmouth since 2016, involving Combined radium. There were also 1 monitoring or reporting violation, which are about late or missing tests and notices.
Nearby cities
- Galesburg331 mg/LVery hard
- Canton401 mg/LVery hard
- Moline110 mg/LModerately hard
- Silvis212 mg/LVery hard
- Kewanee54 mg/LSoft
- East Moline192 mg/LVery hard
- Bartonville283 mg/LVery hard
- Peoria272 mg/LVery hard
- Pekin361 mg/LVery hard
- East Peoria361 mg/LVery hard
Hardness data: TapWaterData US Water Hardness (calculated from utility data, May 10, 2022), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.