How hard is the water in Pennington County, SD?
12.4 grains per gallon
A softener will pay its way here.
The median hardness measured in Pennington County, SD is 213 mg/L as calcium carbonate, which is 12.4 gpg. That is very hard on the USGS scale. It comes from 104 samples at 76 sites between 1990 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 10.6 and 27.7 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 12.4 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 2.1 to 135.8 gpg
The softest single sample on record in Pennington County was 36.7 mg/L and the hardest 2,325 mg/L, a 63-fold gap. The top quarter of sites read above 27.7 gpg and the bottom quarter below 10.6 gpg. So even here some sites draw water soft enough to need nothing at all.
Wells 12.4 gpg, rivers and lakes 11.3 gpg
104 groundwater samples from 76 wells put the median at 213 mg/L. 876 surface samples from 81 sites put it at 194 mg/L. In Pennington County the wells come out 1.1 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 272 lb of salt a year (7 bags of 40 lb, about $49), 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 $149 a year.
Sizing at 12.4 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 744 | 24,000 | 91 lb |
| 2 | 1,488 | 24,000 | 181 lb |
| 4 | 2,976 | 24,000 | 362 lb |
| 6 | 4,464 | 32,000 | 543 lb |
Pennington County against the rest of South Dakota
Among the 55 South Dakota counties with data, Pennington County is number 44 of 55 counting from the hardest. Across the whole country it is harder than 60% of counties.
Softest in South Dakota: Dewey County at 0.5 gpg. Hardest: Hanson County at 84.7 gpg. Closest to Pennington County: Walworth County (13.4), Gregory County (11.1), Harding County (14).