Hard water in Cottage Grove, MN
Reported by Cottage Grove · February 2025
- MN typical
- 160 mg/L
- EPA health violations since 2016
- 0
- Softener for 3 people
- 32k grain
- Data
- Utility report
Tap water in Cottage Grove has about 330 mg/L of hardness, which is 19.3 grains per gallon. On the USGS scale that counts as very hard. The number comes from Cottage Grove, dated February 2025.
At 330 mg/L, Cottage Grove is 170 mg/L above the typical Minnesota figure of 160. None of the 10 nearest cities we track has harder water. The range nearby runs from 56 mg/L in North St. Paul to 270 in Hastings.
What 330 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 330 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 × 19.3 gpg = 4,342 grains a day. A 32,000-grain unit regenerates about every 7 days.
EPA record for Cottage Grove's water system
No health-based violations since 2016
Serves about 42,760 people from groundwater.
- 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 Cottage Grove water hard?
Yes. It measures about 330 mg/L (19.3 grains per gallon), which the USGS classes as very hard.
What is the water hardness in Cottage Grove in grains per gallon?
About 19.3 gpg. One grain per gallon equals 17.1 mg/L, so 330 mg/L divided by 17.1 gives 19.3.
What size water softener do I need in Cottage Grove?
For 3 people using 75 gallons each per day, 19.3 gpg works out to about 4,342 grains a day. A 32,000-grain softener covers that with a regeneration about every 7 days.
Has the Cottage Grove water system had EPA violations?
EPA records show no health-based violations for Cottage Grove since 2016.
Nearby cities
- Hastings270 mg/LVery hard
- Woodbury160 mg/LHard
- Inver Grove Heights270 mg/LVery hard
- Rosemount270 mg/LVery hard
- Lake Elmo249 mg/LVery hard
- Eagan132 mg/LHard
- St. Paul82 mg/LModerately hard
- North St. Paul56 mg/LSoft
- Maplewood56 mg/LSoft
- Farmington270 mg/LVery hard
Hardness data: TapWaterData US Water Hardness (utility report, February 5, 2025), CC BY 4.0. Population: US Census Bureau. Violations: EPA ECHO. How we use them.