How hard is the water in Fond du Lac County, WI?
27.4 grains per gallon
A softener will pay its way here.
The median hardness measured in Fond du Lac County, WI is 469 mg/L as calcium carbonate, which is 27.4 gpg. That is very hard on the USGS scale. It comes from 19 samples at 13 sites between 1990 and 2026, 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 22.2 and 30.8 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 27.4 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 18.5 to 87.6 gpg
The softest single sample on record in Fond du Lac County was 317 mg/L and the hardest 1,500 mg/L, a 5-fold gap. The top quarter of sites read above 30.8 gpg and the bottom quarter below 22.2 gpg.
Wells 27.4 gpg, rivers and lakes 21.5 gpg
19 groundwater samples from 13 wells put the median at 469 mg/L. 79 surface samples from 34 sites put it at 368.5 mg/L. In Fond du Lac County the wells come out 5.9 gpg harder. Groundwater sits in contact with rock for years and picks up calcium and magnesium as it goes, so wells usually read harder. A utility here that draws from the river can deliver noticeably different water from a private well next door.
What a softener would cost to run
For a household of 3, a 40,000-grain unit covers a week between regenerations. Expect about 598 lb of salt a year (15 bags of 40 lb, about $108), 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 $208 a year.
Sizing at 27.4 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 1,644 | 24,000 | 200 lb |
| 2 | 3,288 | 24,000 | 400 lb |
| 4 | 6,576 | 48,000 | 800 lb |
| 6 | 9,864 | 80,000 | 1,200 lb |
Fond du Lac County against the rest of Wisconsin
Among the 72 Wisconsin counties with data, Fond du Lac County is number 3 of 72 counting from the hardest. Across the whole country it is harder than 93% of counties.
Softest in Wisconsin: Vilas County at 1.4 gpg. Hardest: Calumet County at 28.4 gpg. Closest to Fond du Lac County: Lafayette County (27.5), Calumet County (28.4), Waukesha County (23.4).