How hard is the water in Roberts County, SD?
38 grains per gallon
A softener will pay its way here.
The median hardness measured in Roberts County, SD is 650 mg/L as calcium carbonate, which is 38 gpg. That is very hard on the USGS scale. It comes from 216 samples at 213 sites between 1990 and 2022, 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 25.7 and 52 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 38 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 1.0 to 139.6 gpg
The softest single sample on record in Roberts County was 17 mg/L and the hardest 2,390 mg/L, a 141-fold gap. The top quarter of sites read above 52 gpg and the bottom quarter below 25.7 gpg. So even here some sites draw water soft enough to need nothing at all.
Wells 38 gpg, rivers and lakes 34.2 gpg
216 groundwater samples from 213 wells put the median at 650 mg/L. 67 surface samples from 15 sites put it at 585.5 mg/L. In Roberts County the wells come out 3.8 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 48,000-grain unit covers a week between regenerations. Expect about 829 lb of salt a year (21 bags of 40 lb, about $149), 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 $249 a year.
Sizing at 38 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 2,280 | 24,000 | 277 lb |
| 2 | 4,560 | 32,000 | 555 lb |
| 4 | 9,120 | 64,000 | 1,110 lb |
| 6 | 13,680 | twin tank | 1,664 lb |
Roberts County against the rest of South Dakota
Among the 55 South Dakota counties with data, Roberts County is number 13 of 55 counting from the hardest. Across the whole country it is harder than 97% of counties.
Softest in South Dakota: Dewey County at 0.5 gpg. Hardest: Hanson County at 84.7 gpg. Closest to Roberts County: Marshall County (38.4), Lyman County (40.3), Buffalo County (35.3).