Bigger and more-frequent wildfires threaten water supplies across the US

Wildfires leave behind charred trees and scorched vegetation that impact the streams and rivers providing drinking water to much of the country, and new studies show that contamination could remain for more than a decade.

These findings about the longevity of contamination in the nation's drinking water supplies are especially concerning as climate change and increasingly strong El Niño weather events, which intensify drought conditions , have led to bigger and more frequent wildfires in the U.S. So far in 2026, there have been 68,179 blazes burning more than 9.5 million acres (3.8 million hectares).

After a wildfire sweeps through hillsides and forests, rains carry ash and organic matter into the streams that feed water treatment plants for towns and cities alike. Communities are working to adapt, but it can take years and require stopgap solutions.

People in the City of Las Vegas, New Mexico , went without water for months after the Hermit’s Peak/Calf Canyon wildfire contaminated the Gallinas River in 2022. In the four years since, they’ve had to give residents bottled water and ship tanks in from nearby towns as they collected funds to build a new treatment plant.

Karen Pettine, who has owned the Hillcrest Restaurant for 50 years, said the water crisis forced them to close, sometimes for a week at a time.

“It’s hard to run a restaurant without good water,” she said. “We used some paper plates at times. They brought in semi-truckloads of bottled water. You could pick up four cases at a time. The water situation is ongoing because when it rains, it floods and it brings dirty water down the stream.”

Las Vegas Mayor David Romero said climate change has made the things that used to be reliable less predictable.

“It’s a scary situation that we’re all going to encounter,” he said.

Wildfires are a natural part of forest ecosystems, but an increase in their severity has made areas that capture, filter and regulate the flow of water, known as watersheds, vulnerable, said Amanda Hohner, an assistant professor at Montana State University who specializes in wildfires and water quality.

Forested watersheds provide water to nearly two-thirds of municipalities in the U.S., according to Carli Brucker, lead author of a University of Colorado Boulder study that assessed wildfire-affected water quality in hundreds of burned basins and compared them to unburned areas. Their study found that the impacts can last up to eight years.

Garrett McKay, an assistant professor of civil and environmental engineering at Texas A&M, said utilities are extremely concerned about the impacts wildfires have on water. They’re reaching out to experts like him for help finding different water sources or to learn how to treat the organic matter coming into their plants.

Water treatment facilities that rely on streams and rivers typically treat high quality water, aided by trees and soil that act as a natural filtration system, Brucker said. But wildfires cause spikes in heavy metals or dissolved organic matter, which the plants aren't built to handle, she said.

This can force treatment facilities to shut off the incoming water and resort to other sources, which may not be immediately available, Brucker said. Some have groundwater or reservoir backups, but even those can be impacted.

Reservoirs can serve as a “sedimentation basin” where particles can settle, said Kyle Shimabuku, an assistant professor of civil engineering at Gonzaga University. But sediments from burned vegetation are rich in nutrients, like nitrogen and phosphorus, and as they sit in still water, algal blooms can grow, he said. The algae can make people sick and kill the fish.

Chlorine, routinely used to treat water, also is impacted by wildfires, said McKay at Texas A&M. When facilities add disinfectants, like chlorine, to water, they react with the dissolved organic matter left behind by the fires to form “disinfection byproducts,” which are regulated by the U.S. Environmental Protection Agency because they can cause illnesses, including cancer.

Since plants can't remove the disinfection byproducts, they must get rid of the organic matter before disinfecting the water, which can cause delays in the water supply.

When a 2020 wildfire burned the area around No Name and Grizzly creeks, the primary water sources for the city of Glenwood Springs, Colorado, officials scrambled to protect against sediment expected to wash down the slopes when spring rains arrived. They sought help from the Colorado Water Conservation Board. Within two months, the board authorized an emergency loan of $8 million for improvements to the treatment system.

Fort Collins faced a similar challenge that year when ash and sediment from the Cameron Peak fire forced the city to close its river intake and pull water from the Horsetooth Reservoir, which was safe to use because it's fed by a different watershed.

Las Vegas, New Mexico, was hit harder when the Hermit’s Peak/Calf Canyon fire damaged the Gallinas River watershed in 2022. A massive rainstorm swept ash and sludge from the burn scar into the river and reservoirs, forcing the town to shut down its water treatment plant while they installed additional filters and looked for additional water sources.

As they worked on solutions, a massive flood in 2024 carried more burn debris into the town’s two reservoirs, leaving them with only a few days of safe water. As businesses closed and residents bought bottled water, the town hired trucks to bring 2.2 million gallons (8.3 million liters) of water from nearby towns of Santa Fe and Santa Rosa.

They were hit again in February 2025. Burn scar debris coupled with bad weather and equipment failure caused a pressure drop, which resulted in a monthlong boil-water advisory and more water shipments.

“The February event was probably the scariest,” Romero said.

Ultimately, the state and federal governments allocated $148 million to rebuild the town's treatment plant and help support their efforts to find other options, including drilling wells and reusing water. Groundbreaking on the first phase of their new water treatment plant is slated for Nov. 18, the mayor said.

“We’ve been doing a lot of work for other sources of water and we know with climate change and what we experienced in the past, the Gallinas River is something we can’t depend on forever.”