Outside of Minneapolis—and across Minnesota—A Growing Risk Strikes 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 odor, taste, or color in drinking water. More than one in 10 wells exceeded federal safety limits, according to state data, raising concerns among homeowners and local officials about long-term health risks.

Arsenic is perhaps best known as the “king of poisons,” associated with subtle homicides as far back as ancient Greece and Rome and later with widespread accidental poisonings in the 19th century when it was used as a tint in wallpaper, paints, textiles and even candy.

Today, it is no longer used in consumer products, but it is still hidden in some parts of the country.

Throughout the Gopher State, arsenic occurs naturally in rocks and snow and can leach into groundwater. While residents who rely on city water can be sure they are drinking to standards that comply with the government, those who rely on a private source are responsible for testing themselves.

In Minnesota, that’s over 1 million people, or 22% of the population, making for a huge gap.

What the numbers show

In a dataset of more than 71,000 private wells tested across Minnesota, approximately 35,000 (or 48.6%) showed arsenic above 2 µg/L, and 8,264 wells (11.5%) entered above 10 µg/L.

Any amount of arsenic in water may 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 has set a health goal of zero, citing research that shows even low-level exposure over many years may increase the risk of cancer.

In the Minnesota 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 a clustering of many sources near the low point, but a meaningful fractional spike at the highest point.

The pattern is visible even in Minnesota’s densely populated areas. In Hennepin County, just over 71% of wells tested had arsenic greater than 2 µg/L, and 17.6% tested greater than 10 µg/L.

But there is an important caveat to the data. These figures come from the Minnesota Department of Health’s dataset of new private wells inspected between August 2008 and December 2021. That means they are not representative of all private wells currently in use across the state. Old sources, untested sources, and sources tested outside this window are not taken here.

What do families do about it?

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

About one-third of respondents reported that they had taken no steps at all to reduce their arsenic exposure, and more than 80% were not testing their wells as often as the state recommends for other contaminants.

The data also showed clear patterns: People with low income or education levels, or those without a personal connection to someone who tested their well, were least likely to enter the treatment system.

Sight was another obstacle. Many who did not take action believed their water was safe or thought arsenic was rare in their area. Others say they don’t know what level is dangerous or are worried that treatment will be expensive.

These are important results, given that arsenic can be reduced with specific home treatment programs. Minnesota also offers programs designed to help homeowners manage costs, such as Clean Water grants, and the state’s Fix Up Home Improvement Loan program, which offers loans ranging from $2,000 to $75,000 with repayment terms of one to 20 years.

Why does arsenic appear in well water?

In many parts of Minnesota, arsenic occurs in rocks and soil and can dissolve in 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 dug; testing is the only way to know what is coming out of your faucet.

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

The layers of ice—layers of sand, gravel, silt, and clay—can vary significantly in thickness across a region, adding another layer of variability to what a given source may extract. That resulted in a median arsenic level comfortably below 2 µg/L but a 95th percentile level as high as 19.1 µg/L.

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

Start by testing, because that’s the only way to know what’s in your water. The Minnesota Department of Health recommends that users of private wells be tested for arsenic at least once by an approved laboratory, and many states can help refer residents to local testing services or kits.

If arsenic appears in your results, especially if your source is new, consider confirming the findings. MDH notes that arsenic levels can change in the first months after a well is built, so retesting about six months after construction can help confirm whether initial readings indicate a stable, ongoing exposure risk.

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

Even if your result is below that limit, the exposure level can still be dangerous due to cumulative exposure over time. That means you may still want to take action, especially if you have small children, pregnant people, or anyone who relies on a well as their primary source of drinking water.

If you decide to treat water, the most recommended options include systems such as reverse osmosis (often installed in the kitchen sink for drinking and cooking water), immersion distillation, oxidation filtration, adsorptive media, and anion exchange. The right method depends on the specific type 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.