Outside Minneapolis—and Across Minnesota—a Growing Danger Is Hitting Homeowners

Across Minnesota, nearly half of all new private wells tested in recent years have shown traces of arsenic—an invisible toxin that has no smell, taste, or color in drinking water. More than 1 in 10 wells exceeded the federal safety limit, according to state data, raising concerns among homeowners and local officials about long-term health risks.

Arsenic might be best known as the “king of poisons,” linked to covert killings as far back as ancient Greece and Rome and later to widespread accidental poisonings in the 19th century when it was used as a tint in wallpapers, pigments, fabrics, and even candies.

Today, it’s no longer used in consumer products, but it’s still lurking in some parts of the country.

Throughout the Gopher State, arsenic occurs naturally in bedrock and glacial deposits and can leach into groundwater. While residents who rely on the city’s water supply can rest assured that they’re drinking federally compliant levels, those who rely on a private well are responsible for their own testing.

In Minnesota, that’s more than 1 million people, or 22% of the population, creating a major gap.

What the numbers show

In a dataset of over 71,000 new private wells tested throughout Minnesota, almost 35,000 (or 48.6%) showed arsenic above 2 µg/L, and 8,264 wells (11.5%) came in above 10 µg/L.

Any amount of arsenic in the water is likely to cause some concern, and understandably so. The Environmental Protection Agency allows up to 10 micrograms per liter (µg/L) of arsenic in public water systems, but it’s set a health goal of zero, citing research that even low-level exposure over many years can raise the risk of cancer.

In Minnesota’s dataset, the 95th percentile arsenic reading was as high as 18.6 µg/L, while the median result was less than or equal to 2.0 µg/L, indicating many wells cluster near the low end, but a meaningful slice spike into much higher territory.

The pattern shows up even in Minnesota’s most populous areas. In Hennepin County, just over 71% of wells tested had arsenic above 2 µg/L, and 17.6% tested above 10 µg/L.

But there’s an important caveat to the data. These figures come from the Minnesota Department of Health’s dataset of new private wells tested between August 2008 and December 2021. That means it does not represent every private well currently in use across the state. Older wells, untested wells, and wells tested outside this window aren’t captured here.

What households are doing about it

In 2016, the Minnesota Department of Health surveyed nearly 4,000 households with private wells that had tested above the EPA's public water standard for arsenic. The results revealed a troubling disconnect between awareness and action. 

About a third of respondents reported taking no steps at all to reduce their arsenic exposure, and more than 80% weren’t testing their wells as frequently as the state recommends for other contaminants.

The data also showed clear patterns: People with lower incomes or education levels, or those without a personal connection to someone who had tested their well, were significantly less likely to install a treatment system. 

Perception was another barrier. Many who took no action believed their water was safe or assumed arsenic wasn’t common in their area. Others said they didn’t know what level was dangerous or worried that treatment would be too expensive.

They’re significant findings, given that arsenic can often be reduced with relatively straightforward home treatment systems. Minnesota also offers programs designed to help homeowners manage the expense, like Clean Water Grants, as well as the state’s Fix Up Home Improvement Loan program, which provides loans ranging from $2,000 to $75,000 with repayment terms of one to 20 years.

Why arsenic shows up in well water

In many parts of Minnesota, arsenic occurs in rocks and soils and can dissolve into groundwater as water moves through different geologic layers. And because those conditions vary underground, you can’t reliably predict arsenic levels before a well is drilled; testing is the only way to know what’s coming out of your tap.

In Scott County, for example, which aquifer a private well draws from depends largely on the geology of where the home sits. County materials note that the most common drinking-water sources for private wells include unconsolidated glacial deposits and the Prairie du Chien and Jordan aquifers. 

The glacial deposits—layers of sand, gravel, silt, and clay—can vary dramatically in thickness across the county, which adds another layer of variability to what a given well may pick up. That’s resulted in a median arsenic level comfortably below the 2 µg/L but a 95th percentile rate as high as 19.1 µg/L.

If you have a private well, here’s what to do now

Start with testing, because it is the only way to know what’s in your water. The Minnesota Department of Health recommends that private well users test for arsenic at least once through an accredited laboratory, and many counties can help point residents to local testing services or kits.

If arsenic shows up in your results, especially if your well is new, consider confirming the finding. MDH notes that arsenic levels can shift in the early months after a well is constructed, so a retest about six months after construction can help verify whether the initial reading reflects a stable, ongoing exposure risk.

What to do next depends on the levels of arsenic in your water. If your well tests above 10 µg/L, MDH strongly advises installing a treatment system or switching to an alternative drinking-water source for cooking and drinking.

Even if your result is below that threshold, a detectable level can still pose risk due to cumulative exposure over time. That means you may still want to take action, especially if you have young children, people who are pregnant, or anyone relying on the well as their primary source of drinking water.

If you decide to treat the water, the most commonly recommended options include systems like reverse osmosis (often installed at the kitchen sink for drinking and cooking water), distillation, oxidation filtration, adsorptive media, and anion exchange. The right approach depends on the specific form of arsenic in your water and the overall chemistry of your well, so it’s worth matching any system to your lab report rather than buying a one-size-fits-all solution.