How hard is the water in Marshall County, SD?
38.4 grains per gallon
A softener will pay its way here.
The median hardness measured in Marshall County, SD is 658 mg/L as calcium carbonate, which is 38.4 gpg. That is very hard on the USGS scale. It comes from 27 samples at 18 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 23.7 and 47.2 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 38.4 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 3.9 to 88.2 gpg
The softest single sample on record in Marshall County was 67.5 mg/L and the hardest 1,510 mg/L, a 22-fold gap. The top quarter of sites read above 47.2 gpg and the bottom quarter below 23.7 gpg.
Wells 3.9 gpg, rivers and lakes 40 gpg
1 groundwater samples from 1 wells put the median at 67.5 mg/L. 26 surface samples from 17 sites put it at 685 mg/L. In Marshall County the rivers and lakes come out 36.1 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 64,000-grain unit covers a week between regenerations. Expect about 839 lb of salt a year (21 bags of 40 lb, about $151), 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 $251 a year.
Sizing at 38.4 gpg
| People | Grains a day | Unit | Salt a year |
|---|---|---|---|
| 1 | 2,304 | 24,000 | 280 lb |
| 2 | 4,608 | 40,000 | 561 lb |
| 4 | 9,216 | 80,000 | 1,121 lb |
| 6 | 13,824 | twin tank | 1,682 lb |
Marshall County against the rest of South Dakota
Among the 55 South Dakota counties with data, Marshall County is number 12 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 Marshall County: Roberts County (38), Lyman County (40.3), Buffalo County (35.3).