How hard is the water in Dewey County, SD?

0.5 grains per gallon

You do not need a softener here.

The median hardness measured in Dewey County, SD is 8 mg/L as calcium carbonate, which is 0.5 gpg. That is soft on the USGS scale. It comes from 6 samples at 6 sites between 1990 and 2014, 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 0.5 and 36.7 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: medium (how it is measured).

What to do next

You can skip the softener. At 0.5 gpg the most a softener would fix is the odd water spot. If a salesperson in Dewey County says otherwise, ask to see their reading in grains per gallon and compare it with this one. Because Dewey County straddles a decision line, check your own tap with a $10 test strip before you spend anything.

More on when a softener is not worth it.

From 0.4 to 77.7 gpg

The softest single sample on record in Dewey County was 7 mg/L and the hardest 1,330 mg/L, a 190-fold gap. The top quarter of sites read above 36.7 gpg and the bottom quarter below 0.5 gpg. So even in a soft county, a handful of wells here produce water hard enough to scale a heater.

Wells 0.5 gpg, rivers and lakes 15.7 gpg

6 groundwater samples from 6 wells put the median at 8 mg/L. 139 surface samples from 6 sites put it at 269 mg/L. In Dewey County the rivers and lakes come out 15.2 gpg harder. Here the surface water reads harder than the wells, which often points to streams fed by limestone springs or irrigation return flow. A utility here that draws from the aquifer can deliver noticeably different water from a private well next door.

Dewey County against the rest of South Dakota

Among the 55 South Dakota counties with data, Dewey County is the softest. Across the whole country it is harder than 2% of counties.

Hardest: Hanson County at 84.7 gpg. Closest to Dewey County: Ziebach County (0.5), Corson County (1.2), Jackson County (2.7).