How hard is the water in Rock County, MN?
20.5 grains per gallon
A softener will pay its way here.
The median hardness measured in Rock County, MN is 351 mg/L as calcium carbonate, which is 20.5 gpg. That is very hard on the USGS scale. It comes from 18 samples at 17 sites between 1995 and 2023, 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 17.9 and 23 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: medium (how it is measured).
What to do next
At 20.5 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 14.8 to 109.8 gpg
The softest single sample on record in Rock County was 253 mg/L and the hardest 1,880 mg/L, a 7-fold gap. The top quarter of sites read above 23 gpg and the bottom quarter below 17.9 gpg.
Wells 20.5 gpg, rivers and lakes 24.7 gpg
18 groundwater samples from 17 wells put the median at 351 mg/L. 46 surface samples from 12 sites put it at 422 mg/L. In Rock County the rivers and lakes come out 4.2 gpg harder. Here the surface water reads harder than the wells, which often points to streams fed by limestone springs or irrigation return flow. A utility here that draws from the aquifer can deliver noticeably different water from a private well next door.
What a softener would cost to run
For a household of 3, a 32,000-grain unit covers a week between regenerations. Expect about 448 lb of salt a year (12 bags of 40 lb, about $81), 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 $181 a year.
Sizing at 20.5 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 1,230 | 24,000 | 150 lb |
| 2 | 2,460 | 24,000 | 299 lb |
| 4 | 4,920 | 40,000 | 599 lb |
| 6 | 7,380 | 64,000 | 898 lb |
Rock County against the rest of Minnesota
Among the 87 Minnesota counties with data, Rock County is number 24 of 87 counting from the hardest. Across the whole country it is harder than 85% of counties.
Softest in Minnesota: Lake County at 1.3 gpg. Hardest: Traverse County at 42.6 gpg. Closest to Rock County: Stevens County (20.4), Rice County (20.9), Clay County (21).