Wildfire contamination can linger in drinking water for over a decade

Las Vegas, New Mexico, to break ground Nov. 18 on water plant

Wildfires strip charred trees and scorched vegetation from hillsides and forests, and the ash and organic matter that rains then wash into streams and rivers end up in the drinking water supplied to much of the country. New research indicates that contamination of those waterways can persist for more than a decade. The findings arrive as climate change and increasingly strong El Niño weather events, which intensify drought conditions, have produced bigger and more frequent wildfires in the U.S. — 68,179 blazes have burned more than 9.5 million acres so far in 2026.

After a fire sweeps through a watershed, runoff carries ash and organic matter into the streams that feed treatment plants serving towns and cities. Utilities have worked to adapt, but the work can take years and often relies on stopgap solutions.

Wildfires are a natural part of forest ecosystems, but an increase in their severity has left 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 supply 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 with unburned areas. The study found that the impacts can last up to eight years.

Treatment plants that rely on streams and rivers typically receive high-quality water, aided by trees and soil that act as a natural filtration system, Brucker said. Wildfires cause spikes in heavy metals or dissolved organic matter that those plants are not built to handle, she said. A spike can force a facility to shut off its incoming water and turn to other sources, which may not be immediately available; some plants hold groundwater or reservoir backups, but even those can be affected.

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. Utilities are 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.

Reservoirs can serve as a “sedimentation basin” where particles settle out of the water, said Kyle Shimabuku, an assistant professor of civil engineering at Gonzaga University. But sediments from burned vegetation are rich in nutrients such as 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, is also affected by wildfires, McKay said. When facilities add disinfectants such as chlorine, the chemical reacts with the dissolved organic matter left behind by fires to form “disinfection byproducts,” which the U.S. Environmental Protection Agency regulates because they can cause illnesses, including cancer. Because plants cannot remove those byproducts, they must remove the organic matter before disinfecting the water, which can delay the water supply.

Implementing those fixes can cost facilities millions. When a 2020 wildfire burned the area around No Name and Grizzly creeks, the primary water sources for Glenwood Springs, Colorado, local officials prepared for sediment expected to wash down the slopes when spring rains arrived and 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, Colorado, 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 is fed by a different watershed.

Las Vegas, New Mexico, saw its Gallinas River watershed damaged by the Hermit’s Peak/Calf Canyon fire in 2022, and people in the city went without water for months. A massive rainstorm later swept ash and sludge from the burn scar into the river and reservoirs, forcing the town to shut down its water treatment plant while crews installed additional filters and looked for additional water sources.

As those solutions were being pursued, 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 of water from the nearby towns of Santa Fe and Santa Rosa.

The town was hit again in February 2025, when burn scar debris coupled with bad weather and equipment failure caused a pressure drop, resulting in a monthlong boil-water advisory and more water shipments.

In the four years since the fire, Las Vegas has given residents bottled water and shipped tanks in from nearby towns as it collected funds to build a new treatment plant. Karen Pettine, who has owned the Hillcrest Restaurant for 50 years, said the water crisis forced the restaurant 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.”

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.

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. “The February event was probably the scariest.”

Romero said the town has been working on other sources of water: “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.”