What falling wildfire ash means for Minnesotans who get their drinking water from lakes

As wildfire smoke begins to lift from northern Minnesota, scientists and water managers are keeping a close eye on how several days of smoke and falling ash could affect nearby drinking water sources. 

“Most advanced treatment systems could likely handle the impacts of smoke deposition on these lakes,” said Chris Filstrup, a lakes and streams scientist at the University of Minnesota-Duluth. “But I think there’s more concern for smoke exposure in rural areas where maybe there isn’t an advanced treatment system, and what those impacts might look like.”

The fires were sparked by lightning storms in the Boundary Waters Canoe Area Wilderness and Superior National Forest on July 7 and have burned more than 75,000 acres as of July 22. Flames are expected to last through the summer. 

As wildfires burn, they release a mixture of toxic compounds like heavy metals, mercury and carcinogenic chemicals that form from burning organic matter. These toxic compounds can pollute lakes, rivers and streams during wildfires, harming fish and plants. 

They can also affect drinking water systems in communities like Ely that rely on surface water. Ely is one of just 23 Minnesota communities that gets its drinking water from an aboveground lake or river rather than an underground aquifer. 

Related: The smoky season in Minnesota has just begun as wildfires spread

Clerk-treasurer Harold Langowski who oversees Ely’s water operations told MinnPost he is not yet concerned about any drinking water issues from the wildfires, even as ash rained down on the surface of Burntside Lake – where Ely gets its water from – last week. 

That’s because their water treatment facility pumps water from far below the surface of Burntside Lake, meaning any smoke or ash deposits are less concentrated once they move into Ely’s water storage tanks. These tanks are covered and sealed to protect them from external contaminants.

The city’s filtration plant continuously monitors the water’s acidity and turbidity (how cloudy the water is), alerting facility workers if there are contamination problems. They can alter treatment if they notice more organic matter or turbidity coming into their source water, and the Minnesota Department of Health can take samples of that water to ensure it’s safe to drink. 

“We are in close contact with the Department of Health concerning this fire,” Langowski said. 

Concerns for private water sources 

But for Minnesotans who rely on private drinking water systems, wildfire contamination could be a greater threat, experts warned. 

“I mostly worry about cabin country, thinking about people that have maybe been there for a while and are pulling water in off of the lakes and have very minimal treatment systems,” Filstrup said. People with private drinking water systems do not have the same protections that public water systems do, requiring that they monitor the water themselves. Filstrup recommends residents with these surface water treatment systems avoid using that water for drinking during the wildfires. 

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Similar precautions should also be taken by well users, who make up about one in every five Minnesotans. 

“If they have a fire in their area that’s moved across where they get their drinking water or where their well is located, they need to do a physical inspection of their well,” said Kim Larsen, supervisor of the Community Public Water Supply Unit for Minnesota Department of Health. “And once they turn the water on, if they notice any odors or colors, they should definitely have it tested.”

The Community Public Water Supply Unit makes sure Minnesota’s community water supplies are in compliance with the federal Safe Drinking Water Act. This law does not regulate private wells, putting the onus on well owners to address any drinking water contaminants. That’s why Larsen recommends well users take extra precautions during wildfires. 

An uncertain future 

The wildfires burning in northern Minnesota could represent a new norm for the state as climate change drives hotter weather, drying out forests and extending the fire season. The fires currently burning have coincided with an unusual stretch of above average heat throughout the state – virtually every Minnesota weather station has recorded temperatures in the 90s most days since July 11.

To Filstrup, this new reality makes it even more important to study how wildfires and wildfire smoke will affect Minnesota’s lakes and streams, and the drinking water systems that rely on that water. 

“I think this is an area of science that’s kind of at its infancy [in Minnesota], and we just don’t know a whole lot yet,” Filstrup said.

Claire Carlson is a Report for America corps member, covering drinking water for MinnPost in Minnesota. Report for America places talented journalists in local newsrooms to report on under-covered issues and regions.

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