Potter County, South Dakota: Private Well Water Quality
USGS models estimate the private-well arsenic exposure across Potter County, and USGS laboratory samples from at least 7 wells in the county show measured nitrate, manganese, iron and pH. The arsenic figure is an area estimate; the measurements are of other wells — neither is a test of your own well.
This is a modeled probability for the area, not a measurement of your well. USGS statistical models estimate how many private wells in this area are likely to exceed the federal limit — they cannot tell you what is in your water. Two neighbors can have very different results. The only way to know your well is to test it.
~0
people estimated to rely on private wells with modeled arsenic above the 10 µg/L EPA limit
0–0
90% confidence range for that estimate
43% of wells
sampled by USGS in the county measured > 300 µg/L for manganese (7 wells)
Find out what's actually in your well
Private wells are not regulated by the EPA — nobody tests wells in Potter County for you. Arsenic, nitrate and coliform bacteria are the three most common private-well problems, and none of them has a taste or smell. A certified lab test checks all of them at once; the CDC and EPA recommend testing every well at least once a year.
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Measured well tests in Potter County
Unlike the arsenic estimate above, these are real laboratory results: the USGS has published chemistry from at least 7 wells in Potter County, sampled 2005–2012. They describe other wells in the county — domestic, public-supply and monitoring wells — not your well.
| Parameter | Median | Wells over threshold | What the threshold means |
|---|---|---|---|
| Nitrate (as N) | Not enough USGS well samples in Potter County (fewer than 5) — see the state page. | ||
| Manganese7 wells | 125 µg/L90th pct: 633 µg/L | 43%Elevated | > 300 µg/L (EPA health advisory). Lifetime health advisory; above 50 µg/L it already stains fixtures and tastes metallic. Neurological concern for infants. |
| Iron | Not enough USGS well samples in Potter County (fewer than 5) — see the state page. | ||
| pH | Not enough USGS well samples in Potter County (fewer than 5) — see the state page. | ||
What the samples show
- Nitrate (as N): Not enough USGS well samples in Potter County — see the state page.
- Manganese: Manganese is widespread: 43% of sampled wells exceeded the 300 µg/L health advisory and 57% would stain fixtures (median 125 µg/L).
- Iron: Not enough USGS well samples in Potter County — see the state page.
- pH: Not enough USGS well samples in Potter County — see the state page.
- Arsenic (measured, 7 wells): Measured arsenic was low in most sampled wells (median 1 µg/L; 0% over the limit).
What to do about the biggest finding (manganese): Test for manganese; treat with an oxidizing (greensand / birm) filter or a softener for the whole house, plus reverse osmosis at the kitchen tap for drinking.
Source: USGS well samples aggregated to Potter County, South Dakota — manganese, pH and arsenic from USGS ScienceBase 5f36baa782cee144fb3873e8 (site medians, 1988–2019); nitrate and iron from McMahon et al. (2019), Environ. Sci. Technol. 53:29–38 (NWIS wells). County assignment by Census 2020 boundaries. Statistics shown only where ≥ 5 wells were sampled. USGS well samples; not a test of your well.
What the arsenic estimate means
Arsenic occurs naturally in bedrock and can dissolve into groundwater, so it shows up in private wells with no color, taste or smell. The USGS estimate above combines a statistical model of arsenic probability with the number of people on domestic wells in Potter County. A higher number means more of your neighbors are likely drinking water over the federal limit — but your own well could be higher or lower. Long-term arsenic exposure is linked to skin, bladder and lung cancers, so the EPA sets the limit at 10 µg/L.
Statewide, South Dakota also has a modeled nitrate exceedance of 0.1% of private-well residents — worth testing for at the same time.
What to do
- Test your well for arsenic, nitrate, manganese and iron — it's the only way to know your actual level.
- If arsenic or nitrate is present, install a reverse-osmosis system — carbon pitchers do not remove either.
- For manganese or iron staining, a whole-house oxidizing filter or softener is the fix; RO for the drinking tap.
- Re-test annually; well chemistry changes over time.
Manganese: treat the whole house, then polish the tap
Manganese stains fixtures and laundry from every tap, so a whole-house oxidizing filter or softener is the primary fix. Add reverse osmosis at the kitchen sink for drinking water.
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