Minnesota Private Well Water Risk: Arsenic & Nitrate
These figures are USGS statistical estimates for private (domestic) wells in Minnesota. They describe the area's modeled risk — not any single well.
Quick answer: Yes — arsenic occurs naturally in Minnesota groundwater. USGS modeling estimates about 80,354 Minnesota residents rely on private wells with arsenic above the EPA limit of 10 µg/L. The highest modeled exposure is in Blue Earth County (~4,305), St. Louis County (~3,598), Anoka County (~2,983). For nitrate, about 0% of Minnesota's ~1,110,000 private-well residents are modeled above the 10 mg/L limit. These are area estimates, not a test of your well — arsenic has no taste or smell, so only a certified lab test tells you your level.
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.
Nitrate
0%
of the private-well population is modeled above the 10 mg/L nitrate limit
~441
people on wells estimated above the limit
~1,110,000
total residents on private wells statewide
Source: USGS machine-learning nitrate model, Ransom et al. (2022), domestic-well depth zone.
Find out what's actually in your well
Minnesota has one of the higher modeled arsenic exposures in the country — but that number is an area estimate, not your well. 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.
Basic screening only. Confirm arsenic, nitrate and bacteria with a certified lab.
Find a certified drinking-water labAmazon links are affiliate links — we may earn a commission at no extra cost to you.
Arsenic
Across Minnesota, an estimated ~80,354 people rely on private wells with modeled arsenic above the 10 µg/L EPA limit. The highest modeled exposure is in Blue Earth County (~4,305 people).
Counties with the highest modeled arsenic exposure
| County | Est. well residents over arsenic limit | 90% range |
|---|---|---|
| Blue Earth County | ~4,305 | 3,440–5,295 |
| St. Louis County | ~3,598 | 2,942–4,425 |
| Anoka County | ~2,983 | 2,310–3,858 |
| Crow Wing County | ~2,657 | 1,973–3,570 |
| Nicollet County | ~2,248 | 1,768–2,770 |
| Sibley County | ~2,193 | 1,747–2,682 |
| Sherburne County | ~2,191 | 1,701–2,799 |
| Otter Tail County | ~1,909 | 1,478–2,480 |
| Wright County | ~1,877 | 1,490–2,384 |
| Redwood County | ~1,865 | 1,543–2,214 |
| Beltrami County | ~1,827 | 1,392–2,396 |
| Brown County | ~1,764 | 1,448–2,100 |
| Itasca County | ~1,651 | 1,311–2,088 |
| Freeborn County | ~1,637 | 1,267–2,084 |
| Washington County | ~1,561 | 1,189–2,062 |
| Le Sueur County | ~1,547 | 1,226–1,939 |
| Faribault County | ~1,464 | 1,160–1,788 |
| Waseca County | ~1,434 | 1,130–1,792 |
| McLeod County | ~1,406 | 1,191–1,662 |
| Benton County | ~1,376 | 1,092–1,727 |
| Cass County | ~1,358 | 1,035–1,794 |
| Chisago County | ~1,353 | 1,052–1,745 |
| Isanti County | ~1,346 | 1,064–1,700 |
| Jackson County | ~1,337 | 1,067–1,641 |
| Pine County | ~1,328 | 1,099–1,609 |
| Polk County | ~1,312 | 1,099–1,559 |
| Rice County | ~1,277 | 1,070–1,531 |
| Mille Lacs County | ~1,266 | 992–1,625 |
| Todd County | ~1,263 | 1,005–1,582 |
| Douglas County | ~1,252 | 958–1,643 |
| Stearns County | ~1,218 | 980–1,522 |
| Roseau County | ~1,190 | 960–1,464 |
| Martin County | ~1,185 | 954–1,455 |
| Morrison County | ~1,176 | 933–1,487 |
| Kandiyohi County | ~1,166 | 948–1,443 |
| Becker County | ~1,131 | 879–1,465 |
| Meeker County | ~1,095 | 916–1,314 |
| Aitkin County | ~1,054 | 824–1,356 |
| Carlton County | ~1,028 | 853–1,246 |
| Renville County | ~982 | 817–1,170 |
| Kanabec County | ~893 | 746–1,073 |
| Hubbard County | ~881 | 677–1,152 |
| Scott County | ~881 | 740–1,050 |
| Steele County | ~849 | 688–1,045 |
| Mower County | ~805 | 664–977 |
| Watonwan County | ~684 | 572–813 |
| Pennington County | ~629 | 518–758 |
| Lyon County | ~624 | 538–723 |
| Goodhue County | ~540 | 424–691 |
| Clay County | ~512 | 417–627 |
| Dodge County | ~419 | 351–499 |
| Carver County | ~408 | 340–491 |
| Murray County | ~401 | 344–469 |
| Clearwater County | ~387 | 315–475 |
| Lac qui Parle County | ~387 | 329–455 |
| Olmsted County | ~364 | 294–454 |
| Wadena County | ~352 | 276–448 |
| Pope County | ~334 | 272–413 |
| Lake of the Woods County | ~319 | 252–403 |
| Koochiching County | ~269 | 216–335 |
| Norman County | ~248 | 204–300 |
| Winona County | ~243 | 182–322 |
| Nobles County | ~240 | 198–290 |
| Marshall County | ~224 | 183–273 |
| Chippewa County | ~221 | 188–260 |
| Wabasha County | ~220 | 165–295 |
| Dakota County | ~219 | 176–275 |
| Fillmore County | ~202 | 164–249 |
| Mahnomen County | ~202 | 167–245 |
| Lake County | ~192 | 162–231 |
| Stevens County | ~187 | 155–226 |
| Wilkin County | ~176 | 143–215 |
| Swift County | ~176 | 148–209 |
| Red Lake County | ~163 | 135–194 |
| Houston County | ~157 | 120–206 |
| Grant County | ~129 | 106–157 |
| Big Stone County | ~120 | 102–142 |
| Traverse County | ~117 | 96–144 |
9 additional Minnesota counties have lower modeled arsenic exposure (fewer than 100 estimated well residents over the limit). Of these, 8 have measured USGS well samples: Cook, Cottonwood, Hennepin, Kittson, Pipestone, Ramsey, Rock, Yellow Medicine.
Source: USGS domestic-well arsenic model, Lombard et al. (2021); county population product (2017).
Measured well tests by county
The USGS has published laboratory results from wells in 86 Minnesota counties (at least 5 wells each). These are real measurements of other wells — domestic, public-supply and monitoring wells — not a test of yours. The tables rank counties by the share of sampled wells over each federal threshold.
Nitrate (as N): counties with the most wells > 10 mg/L (EPA MCL)
| County | Wells over | Median | Sampled |
|---|---|---|---|
| Sherburne County | 46% | 8.8 mg/L | 48 wells |
| Otter Tail County | 26% | 1.8 mg/L | 61 wells |
| Polk County | 20% | 1.2 mg/L | 49 wells |
| Blue Earth County | 15% | 2.2 mg/L | 13 wells |
| Yellow Medicine County | 13% | 0 mg/L | 15 wells |
| Stearns County | 13% | 3.9 mg/L | 8 wells |
| Dakota County | 12% | 0.3 mg/L | 78 wells |
| Goodhue County | 11% | 2.4 mg/L | 44 wells |
| Rock County | 11% | 0.7 mg/L | 9 wells |
| Aitkin County | 9% | 0 mg/L | 11 wells |
Manganese: counties with the most wells > 300 µg/L (EPA health advisory)
| County | Wells over | Median | Sampled |
|---|---|---|---|
| Renville County | 71% | 471 µg/L | 7 wells |
| Hennepin County | 64% | 536 µg/L | 72 wells |
| Becker County | 60% | 410 µg/L | 5 wells |
| Ramsey County | 56% | 342 µg/L | 25 wells |
| Rock County | 50% | 305 µg/L | 16 wells |
| Hubbard County | 50% | 244 µg/L | 6 wells |
| Anoka County | 47% | 292 µg/L | 57 wells |
| Blue Earth County | 46% | 110 µg/L | 13 wells |
| Crow Wing County | 44% | 205 µg/L | 16 wells |
| Meeker County | 43% | 233 µg/L | 7 wells |
Source: USGS ScienceBase 5f36baa782cee144fb3873e8 (manganese, pH, arsenic) and McMahon et al. (2019), Environ. Sci. Technol. 53:29–38 (nitrate, iron); aggregated by county with Census 2020 boundaries. USGS well samples; not a test of your well.
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Minnesota well water: FAQ
Is there arsenic in well water in Minnesota?
Yes. USGS modeling estimates about 80,354 people in Minnesota use private wells with arsenic above 10 µg/L, across 87 modeled counties. Arsenic comes from natural bedrock and varies well to well, even between neighbors, so a lab test is the only way to know your own level.
Which Minnesota counties have the most arsenic in well water?
By modeled number of well residents over the arsenic limit: Blue Earth County (~4,305), St. Louis County (~3,598), Anoka County (~2,983). Counties with more private-well users rank higher, so a smaller county can still have a high share of affected wells.
How do I remove arsenic from well water in Minnesota?
Test first. If arsenic is present, a point-of-use reverse-osmosis system under the kitchen sink removes 90%+ of it; boiling does not remove arsenic (it concentrates it), and carbon pitchers and water softeners do not remove it either. Whole-house adsorptive arsenic media is used when levels are high. Re-test after installing and then annually.
Is nitrate a problem in Minnesota well water?
USGS models about 0% of Minnesota's private-well population (~441 people) above the 10 mg/L nitrate limit. Nitrate is highest in shallow wells near fertilized cropland, septic systems or livestock, and matters most for infants and pregnancy.
Do I need an acid neutralizer for my well in Minnesota?
Acidic well water is uncommon in Minnesota, but it does occur. In USGS lab results from 3,581 wells across 86 Minnesota counties, 2% had pH below 6.5. The most acidic sampled counties are Pine County (24% of 17 wells), Crow Wing County (17% of 78 wells), Koochiching County (17% of 6 wells). You only need a neutralizer if your own well tests below about 6.5 — signs include blue-green stains on fixtures and pinhole leaks in copper pipe. A calcite (or calcite/Corosex) neutralizer tank handles mildly acidic water (roughly pH 6–6.5); very acidic water usually needs soda-ash injection. Test first-draw lead and copper too, since acidic water dissolves both from plumbing.
High manganese in Minnesota well water — what should I do?
In USGS lab results from 817 wells across 38 Minnesota counties, 23% were above the EPA's 300 µg/L health advisory for manganese and 57% were above the 50 µg/L level where it stains fixtures and laundry black or brown. Sampled counties with the highest share over the health advisory: Renville County (71% of 7 wells), Hennepin County (64% of 72 wells), Becker County (60% of 5 wells). If your own test is over 300 µg/L, don't use the water for infant formula and use another source for drinking and cooking until it is treated — high manganese is linked to neurological effects, especially in babies and children. Boiling does not remove it. For the whole house, an oxidizing filter (greensand, Birm or air-injection) handles manganese, usually alongside iron; a water softener can remove low levels. For drinking water, a point-of-use reverse osmosis system reduces manganese at the kitchen tap. Retest after treatment to confirm it worked.