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

Wildfires are leaving behind contamination that could persist for over a decade in the nation's drinking water supplies, according to new studies. Climate change and stronger El Niño events have led to an increase in the size and frequency of wildfires in the United States. In 2026 alone, there have been 68,179 wildfires burning more than 14,062 square miles.

When wildfires ravage hillsides and forests, rains carry ash and organic matter into streams that provide water to towns and cities. Communities across the U.S. are adapting to these challenges, but it often requires stopgap solutions and can take years to address the issues fully. For example, residents in Las Vegas, New Mexico, went without water for months after the Hermit's Peak/Calf Canyon wildfire contaminated the Gallinas River in 2022.

They had to provide bottled water and truck in tanks from nearby towns while they built a new treatment plant.

The impacts of wildfires on water quality can last up to eight years, according to a University of Colorado Boulder study led by Carli Brucker. Forested watersheds, which provide water to nearly two-thirds of U.S. municipalities, are vulnerable due to the increases in severity and frequency of wildfires. These watersheds are responsible for filtering and regulating water flow, but the organic matter left behind by fires can overwhelm treatment facilities.

Utilities are reaching out to experts for assistance in finding alternative water sources or learning how to treat the organic matter that enters their systems. High-quality water treatment typically relies on trees and soil for natural filtration, but wildfires disrupt these processes. Heavy metals and dissolved organic matter can cause spikes in pollutants that treatment facilities aren't designed to handle, potentially forcing them to shut off water supplies or resort to less reliable sources.

Adding disinfectants like chlorine to water can also create disinfection byproducts when reacting with the organic matter left behind by wildfires. These byproducts, regulated by the U.S. Environmental Protection Agency, can cause illnesses including cancer. Facilities must remove the organic matter before disinfecting the water, which can cause delays in water supply.

Communities are working to adapt, but the challenges posed by wildfires and climate change remain significant.