How hard is the water in Polk County, MN?
18.5 grains per gallon
A softener will pay its way here.
The median hardness measured in Polk County, MN is 317 mg/L as calcium carbonate, which is 18.5 gpg. That is very hard on the USGS scale. It comes from 76 samples at 73 sites between 1990 and 2025, drawn from groundwater wells, which is what most taps and private wells in the county draw on.
How much it varies here
Half the sites came in between 15.5 and 22.1 gpg. The whole middle of that range gives the same answer, so a test of your own tap is unlikely to change it. Confidence in the county figure: high (how it is measured).
What to do next
At 18.5 gpg a softener pays its way here. Before you buy, check the quoted unit's grain capacity against the sizing table below, and ask whether it regenerates on demand, which uses less salt than a timer. Call your utility for its own report if you are on city water.
More on sizing a softener for your household.
From 5.0 to 77.1 gpg
The softest single sample on record in Polk County was 86 mg/L and the hardest 1,320 mg/L, a 15-fold gap. The top quarter of sites read above 22.1 gpg and the bottom quarter below 15.5 gpg.
Wells 18.5 gpg, rivers and lakes 16.1 gpg
76 groundwater samples from 73 wells put the median at 317 mg/L. 267 surface samples from 49 sites put it at 275 mg/L. In Polk County the wells come out 2.4 gpg harder. Groundwater sits in contact with rock for years and picks up calcium and magnesium as it goes, so wells usually read harder. The two sources are close, so the county figure should hold whichever one your tap is on.
What a softener would cost to run
For a household of 3, a 24,000-grain unit covers a week between regenerations. Expect about 404 lb of salt a year (11 bags of 40 lb, about $73), and roughly 2,346 gallons of regeneration water. Installed, most units run $1,000 to $4,500; spread over 15 years with salt, that is about $173 a year.
Sizing at 18.5 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 1,110 | 24,000 | 135 lb |
| 2 | 2,220 | 24,000 | 270 lb |
| 4 | 4,440 | 32,000 | 540 lb |
| 6 | 6,660 | 48,000 | 810 lb |
Polk County against the rest of Minnesota
Among the 87 Minnesota counties with data, Polk County is number 34 of 87 counting from the hardest. Across the whole country it is harder than 80% of counties.
Softest in Minnesota: Lake County at 1.3 gpg. Hardest: Traverse County at 42.6 gpg. Closest to Polk County: Pope County (18.5), Becker County (18.1), Olmsted County (18).