How hard is the water in Minnehaha County, SD?
26 grains per gallon
A softener will pay its way here.
The median hardness measured in Minnehaha County, SD is 445 mg/L as calcium carbonate, which is 26 gpg. That is very hard on the USGS scale. It comes from 895 samples at 14 sites between 1990 and 2014, drawn from every sampling site in the county, wells and surface water together.
How much it varies here
Half the sites came in between 4.3 and 27.4 gpg. That spread crosses a decision line, so some homes here land on a different answer. A $10 test strip on your own tap settles it. Confidence in the county figure: high (how it is measured).
What to do next
At 26 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. Because Minnehaha County straddles a decision line, check your own tap with a $10 test strip before you spend anything.
More on sizing a softener for your household.
From 0.2 to 35.6 gpg
The softest single sample on record in Minnehaha County was 3 mg/L and the hardest 610 mg/L, a 203-fold gap. The top quarter of sites read above 27.4 gpg and the bottom quarter below 4.3 gpg. So even here some sites draw water soft enough to need nothing at all.
Wells 25.9 gpg, rivers and lakes 26.1 gpg
1 groundwater samples from 1 wells put the median at 443 mg/L. 894 surface samples from 13 sites put it at 446.5 mg/L. In Minnehaha County the rivers and lakes come out 0.2 gpg harder. Here the surface water reads harder than the wells, which often points to streams fed by limestone springs or irrigation return flow. 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 40,000-grain unit covers a week between regenerations. Expect about 567 lb of salt a year (15 bags of 40 lb, about $102), 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 $202 a year.
Sizing at 26 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 1,560 | 24,000 | 190 lb |
| 2 | 3,120 | 24,000 | 380 lb |
| 4 | 6,240 | 48,000 | 759 lb |
| 6 | 9,360 | 80,000 | 1,139 lb |
Minnehaha County against the rest of South Dakota
Among the 55 South Dakota counties with data, Minnehaha County is number 24 of 55 counting from the hardest. Across the whole country it is harder than 92% of counties.
Softest in South Dakota: Dewey County at 0.5 gpg. Hardest: Hanson County at 84.7 gpg. Closest to Minnehaha County: Meade County (25.5), Grant County (25.3), Aurora County (25.1).