Hard water in Johnston, IA
Reported by Johnston Municipal Water Supply · August 2025
- IA typical
- 183 mg/L
- EPA health violations since 2016
- 0
- Softener for 3 people
- 24k grain
- Data
- Utility report
Johnston water measures 126 mg/L (7.4 gpg) of hardness, hard by USGS standards. The number comes from Johnston Municipal Water Supply, dated August 2025.
Johnston sits 57 mg/L below the typical Iowa figure of 183. Of the 10 nearest cities we track, 3 have softer water and 7 have harder. The range nearby runs from 68 mg/L in Clive to 302 in Waukee.
What 126 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 126 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 × 7.4 gpg = 1,658 grains a day. A 24,000-grain unit regenerates about every 14 days.
EPA record for Johnston's water system
No health-based violations since 2016
Serves about 24,897 people from surface water.
- 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 Johnston water hard?
Yes. It measures about 126 mg/L (7.4 grains per gallon), which the USGS classes as hard.
What is the water hardness in Johnston in grains per gallon?
About 7.4 gpg. One grain per gallon equals 17.1 mg/L, so 126 mg/L divided by 17.1 gives 7.4.
What size water softener do I need in Johnston?
For 3 people using 75 gallons each per day, 7.4 gpg works out to about 1,658 grains a day. A 24,000-grain softener covers that with a regeneration about every 14 days.
Has the Johnston water system had EPA violations?
EPA records show no health-based violations for Johnston Municipal Water Supply since 2016.
Nearby cities
- Urbandale99 mg/LModerately hard
- Polk City151 mg/LHard
- Clive68 mg/LModerately hard
- Ankeny120 mg/LModerately hard
- Des Moines296 mg/LVery hard
- West Des Moines135 mg/LHard
- Waukee302 mg/LVery hard
- Altoona296 mg/LVery hard
- Norwalk132 mg/LHard
- Ames150 mg/LHard
Hardness data: TapWaterData US Water Hardness (utility report, August 15, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.