Wildfires in the United States are leaving a second disaster behind them: drinking water tainted for years after the flames have gone out. New studies show that contamination from burned landscapes can remain in the rivers and streams that supply towns and cities for more than a decade, a threat that is growing as fires become bigger and more frequent. So far in 2026, there have been 68,179 blazes in the US, burning more than 14,062 square miles.
Forested watersheds provide water to nearly two-thirds of municipalities in the country, according to Carli Brucker, lead author of a University of Colorado Boulder study that assessed water quality in hundreds of burned basins and compared them with unburned areas. Her team found that the effects on water quality can last up to eight years. “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 specialises in wildfires and water quality.
The damage arrives after the fire. Rain washes ash and organic matter from scorched hillsides into the streams that feed treatment plants. Facilities that normally treat high-quality water, helped by trees and soil that act as a natural filter, suddenly face spikes in heavy metals and dissolved organic matter they were not built to handle. Some are forced to shut off their intake and find other sources, which may not be immediately available.
Chlorine, routinely used to treat water, creates a further problem. When disinfectants are added to water carrying dissolved organic matter from burned land, they react to form disinfection byproducts, which the US Environmental Protection Agency regulates because they can cause illness, including cancer. Plants cannot remove those byproducts once formed, so they must strip out the organic matter before disinfecting, which can delay the water supply. Utilities are extremely concerned, said Garrett McKay, an associate professor of civil and environmental engineering at Texas A&M University, and many are turning to experts for help finding different water sources or learning how to treat what is coming into their plants.
The town of Las Vegas, New Mexico, shows how long the crisis can last. After the Hermit’s Peak/Calf Canyon wildfire contaminated the Gallinas River in 2022, residents went without water for months. The town handed out bottled water and trucked in supplies from nearby towns while it raised funds for a new treatment plant. A massive flood in 2024 carried more burn debris into its two reservoirs, leaving only a few days of safe water, and in February 2025 a pressure drop caused by burn-scar debris led to a month-long boil-water advisory. State and federal governments have now allocated $148 million to rebuild the plant and develop other sources, including drilling wells and reusing water. Groundbreaking on the first phase is scheduled for 18 November.
Other towns have faced the same scramble. When a 2020 wildfire burned around the No Name and Grizzly creeks that supply Glenwood Springs, Colorado, the state water board authorised an emergency loan of $8 million for treatment improvements within two months. Fort Collins was forced to close its river intake after ash and sediment from the Cameron Peak fire that year, switching to the Horsetooth Reservoir, which was safe because it is fed by a different watershed.
Climate change and increasingly strong El Niño weather events, which intensify drought, are driving the trend. Las Vegas Mayor David Romero said the experience had changed how the town thinks about its water. “It’s a scary situation that we’re all going to encounter,” he 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.”
Sources: Associated Press, “Bigger and more-frequent wildfires threaten water supplies across the US”, 13 November 2026, https://www.kcau9.com/news/national-news/bigger-and-more-frequent-wildfires-threaten-water-supplies-across-the-us/
