Wildland Fires Could Be Putting Your Drinking Water at Risk

Hotter and more frequent wildfires are threatening water sources in the West. We looked at what the latest research says about protecting them.

By Michael Wandersee, Dara Zimmerman, Kelly Kachurak, Leo Angelo Gumapas, Kayla DeVault Wendt, and Kurt Kesteloot

About this article

This article was originally published in the "Features" section of Park Science magazine, Volume 37, Number 1, Summer 2023 (July 31, 2023).

Glacier National Park after the Reynolds Creek Fire in 2015.

Image credit: NPS / Kayla DeVault Wendt

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Recurring wildland fires are a natural and necessary part of many landscapes in the western United States.

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But decades of fire suppression and a changing climate have made them more destructive than they were historically, putting our supply of safe drinking water at risk. Shawn Norton, Sustainable Operations program manager for the National Park Service, says, “Protection of drinking water is perhaps one of the greatest public trusts.” He says climate change is “altering wildfire regimes and thus water quality,” making it imperative that we understand the risk to drinking water from fires that are now more frequent and intense. Norton adds that we must prepare for this risk by making good public health and engineering decisions. But to do that, it’s important to know how wildfire affects water sources and infrastructure. This isn’t well understood, because there’s not much information to help us assess post-wildfire impacts and recovery. To address this knowledge gap, we examined the latest research regarding wildfire impacts on water quality and identified measures parks can take to reduce risk.

A Natural Process Changes

A synergistic and reinforcing relationship exists between climate change and wildfires, profoundly affecting drinking water quality. Hotter local temperatures, drought, reduced snowpack, less rainfall, extreme flood events, and other consequences of a changing climate have a negative impact on drinking water sources. Less rain and snow reduce the amount of surface and ground water available to recharge sources. We see a similar deficit in the timing and volume of runoff. On the other hand, the anomalies in rainfall and snowpack caused by climate change can lead to sudden, large releases of water when ice or snow melts. The outcome of these events is increased contamination of water supplies, decreased water quality, and increased dependency on electrical systems to provide drinking water.

Periodic wildfires are an integral part of many different ecosystems. They create open habitat, supporting diverse plants and animals that provide benefits to people. But the frequency and severity of wildfires have increased in recent years due to climate change. Higher temperatures resulting from climate change increase the rate of water evaporation, exacerbating the dry soil conditions that lead to increased risk of wildfires. And wildfires exacerbate climate change’s pressures on public drinking water systems. For example, the deposition of fine particulate matter—like ash—and other contaminants from wildfires can affect water quality. This can happen even when a fire occurs a considerable distance away. The result of these reinforcing phenomena is a self-perpetuating cycle of change in climate and wildfire regimes, with damaging effects on water quality.

A drinking water impoundment in Sequoia and Kings Canyon National Park damaged from a mudslide caused by heavy rainfall after the KNP Complex Fire.

Image credit: NPS / Heather Davies

Impaired Health and Function of Water Sources

Fires can affect drinking water sources during and immediately after the fire or for months to years afterwards. The changes these fires cause in water temperature, acid-alkaline balance (pH), and turbidity can overwhelm water treatment facilities. And certain fire-retardant chemicals are persistent contaminants with serious health effects.

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The lightning-caused Moose Creek Fire broke out nearby during the study, causing the observed stream temperature to rise from an average of 46 to a peak of 63 degrees Fahrenheit.

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In a 2001 scientific study at Deadhorse Creek, Montana, researchers measured temperatures in stream surface water. The lightning-caused Moose Creek Fire broke out nearby during the study, causing the observed stream temperature to rise from an average of 46 to a peak of 63 degrees Fahrenheit. Higher temperatures combined with ash deposition correlated with a rise in dissolved ammonia levels. This raised the water’s toxicity, increasing its potential to harm aquatic life.

Water sources—and drinking water—typically have a fairly neutral pH of 6.5 to 7.5. But wildfire ash has a pH of 9 to 13, which is similar to the pH of ammonia or lye—corrosive substances that are highly toxic. Fire retardants used for wildfire control in forest, brush, or grassland, tend to be more acidic. They can have a pH as low as 5.0. When fire retardants run off into rivers and streams, the pH of those water bodies decreases. This causes metals like lead and arsenic, and other harmful compounds, to dissolve into the water. During wildfires, burned infrastructure can also release toxic metals into the environment, which could end up in drinking water sources. Drinking water plants do not typically screen for metals such as these, so they may go undetected. Drastic pH changes may harm wildlife in streams and rivers.

Per- and polyfluorinated alkyl substances (PFAS), “forever chemicals,” are in certain retardants used to combat wildfires. They are persistent in the environment, making it more likely they will enter drinking water sources. PFAS can be toxic to people and wildlife. The United States has phased out the manufacture of two types of PFAS, which are perfluorooctanoic acid (PFOA) and perfluorooctane sulfate (PFOS). But these chemicals are still produced outside of the U.S. and imported into the country in consumer goods. Processes using granulated activated carbon, ion exchange resins, and high-pressure membrane systems are effective at removing PFAS from drinking water. But removing them is expensive.

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Water treatment plants are designed for a narrow range of turbidity, so they can’t manage the increased levels caused by wildfires.

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Wildfires impair watershed function. Wildfire incinerates soil, destroying the organic “glue,” like fungi and tree root elements, that hold soil in place. Destruction of organic matter leads to reduced absorption and retention of water in the soil, and increases in erosion, mudslides, and landslides. Reduced soil absorption causes increased turbidity and flow rates in nearby streams and rivers. Water treatment plants are designed for a narrow range of turbidity, so they can’t manage the increased levels caused by wildfires.

Wildfires also leave ash in place of cohesive soils, destabilizing soil structure. These finer particles are difficult to filter and treat in water treatment plants. Finally, burned areas are darker than the surrounding landscape. Darker landscapes retain heat better, which discourages snow retention and causes it to melt faster, decreasing soil absorption and increasing runoff. Higher water temperature, changes in pH, and incinerated soil matrices have a synergistic effect. They increase metal concentrations, turbidity, and sediment and nutrient loads in waterways, putting life in and outside the water at risk.

Water is less available across much of the western United States because of population pressures, declining snowpack, reduced precipitation from prolonged drought, and higher ambient temperatures. Wildfires that are more frequent and intense exacerbate the problem, increasing the vulnerability of our water sources. Destruction of water catchment areas and soil matrices, darkened soil, sediment impacts on water quality, and PFAS contamination all translate to even less usable water.

Algal Blooms and Stressed Facilities

Burned areas release carbon compounds, which lead to increased organic matter in water. When combined with increased nutrients, higher water temperatures, and reduced water availability from wildfires, this can cause harmful algal blooms to occur. A study of the catastrophic 2019–2020 Australian wildfires confirmed that wildfires increase the risk of harmful blooms through aerosol transport of nutrients like nitrogen, phosphorus, and iron, which feed algae. This study found a connection between wildfire aerosols and oceanic chlorophyll concentration (an indicator of algal activity) miles away from the fires.

Algal bloom from increased nutrients in the Merced River in Yosemite National Park.

Image credit: NPS / Catherine Fong

Algal blooms reduce water flow, further increasing water temperatures and nutrient loading from wildfire ash. When water temperatures are greater than 25 degrees Celsius (77 degrees Fahrenheit), the likelihood of harmful algal blooms increases, which in turn lead to higher temperatures from water stagnation, resulting in a self-perpetuating cycle. The increase in photosynthesis from blooms can also cause cyanotoxins (produced by blue-green algae) to develop, some of which can harm our skin, liver, or nervous system.

The Julius Marshall Water Treatment Plant is the largest tribal water treatment plant within California’s geopolitical boundaries. It is operated by the Hoopa Valley Tribe. The Trinity River supplies water to the plant. When tribal members observed cyanotoxins in the water, they installed a seasonal, summer, ultraviolet-ozone unit to treat them. Initially, the unit was activated based on cyanotoxin presence confirmed through water quality testing. But rising temperatures from wildfires affected the plant’s operations. Now the ultraviolet-ozone unit is turned on continuously from July through October, and the Tribe runs the unit based on the wildfire season instead of on expensive water quality testing.

Increased burned organic matter in waterways may also cause treatment plants to step up carcinogenic disinfection, releasing disinfection byproducts into treated water. These byproducts can change the water’s color and taste, clog filters, and oblige facilities to use additional chemicals and spend more time making water fit for consumption.

Compromised Distribution Systems

Wildfires can damage or destroy the critical infrastructure of water distribution systems, such as piping, pumphouses, booster pumps, and storage tanks. Systems that rely on grid electricity are especially vulnerable. Pumping, treating, and moving water through a distribution system rely on energy, be it electrical or gas. Electrical grids are commonly powered down proactively to reduce the risk of wildfire ignition during periods of severe weather, such as windstorms, dry lightning, and abnormally dry conditions. During periods of extreme fire risk, utility companies may institute public safety power shutoffs to reduce the risk of grid equipment sparking wildfires.

Whiskeytown National Recreation Area had a steel water tank that remained intact after the Carr Fire damaged other infrastructure. The wellhouse and pump burned, depriving users of water for some time.

Image credit: NPS / David Larabee

Shutoffs have become more common since the advent of grid-caused wildfires like the California Camp Fire, which killed 85 people. Communities in fire-prone California may experience multiple shutoffs per month and regular or extended periods without power during consecutive summer and fall months. These power-downs reduce communities’ access to potable water.

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One study showed that soil temperatures during a wildfire reached 600 degrees Celsius (1,112 degrees Fahrenheit) on the surface. This is 28 percent hotter than the daytime surface temperature of Mercury, the planet closest to our sun.

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During fires, superheated plastic pipes can degrade and leach carcinogenic chemicals like benzene, causing significant system failure and requiring a complete pipe network replacement. The extent of the degradation and resulting system repair depend on how intense the wildfire is, how deep the pipes are buried, and what material they’re made of.

One study showed that soil temperatures during a wildfire reached 600 degrees Celsius (1,112 degrees Fahrenheit) on the surface. This is 28 percent hotter than the daytime surface temperature of Mercury, the planet closest to our sun. Below the surface of an active fire, temperatures ranged from 313 degrees Celsius (595 degrees Fahrenheit) to 105 degrees Celsius (221 degrees Fahrenheit) at depths up to 10 cm (4 inches).

Water pipes typically consist of polyvinyl chloride (PVC), ductile iron, polyethylene, or asbestos cement. PVC is stable up to 60 degrees Celsius (140 degrees Fahrenheit). Ductile iron and polyethylene are stable to 100 and 65 degrees Celsius (212 and 150 degrees Fahrenheit), respectively. Most concrete is stable at temperatures as high or higher than 600 degrees Celsius, so buried concrete will likely be unaffected by wildfires. Other types of buried materials will be more susceptible, as will above-ground infrastructure.

Wildfires have multiple kinds of impacts on drinking water sources. Some of these happen during a fire (immediate impacts) or for a long time afterwards (long-term impacts). Some impacts happen as a result of the fire itself (direct impacts) or cascade from changes to the environment brought about by the fire (indirect impacts).

Image credit: U.S Fish and Wildlife Service / Michael Wandersee

Reducing Risk

Steven Rice, a hydrogeologist with the National Park Service, says one difficulty in mitigating impacts on water systems after a wildfire is “the varied timescales that effects are observed.” These can be immediate for infrastructure damage, periodic when dealing with post-fire sedimentation, or long-term, such as reduced recharge to aquifers. And he says, “they may all be occurring simultaneously.”

Water system managers and utilities can reduce the short- and long-term risks to their facilities from wildfires by eliminating risk through design, mitigating risk through material changes, lowering risk through maintenance, or managing risk through operations.

Ways to Reduce Risk

Eliminate risk through design:

• Bury water, power, and gas lines deeper.
• Compare benefits of using more costly, resistant pipe materials, versus cheaper materials at varying depths.
• Ensure backup power sources can run operations for two weeks.
• Construct systems with lower embodied carbon such as steel manufactured from electric arc furnaces using 95% scrap steel or concrete as specified by the General Services Administration.
• Incorporate seasonal treatment systems that adjust treatment based on the varying quality of the influent water. Examples are carbon filters and ultraviolet/ozone generators for deactivating toxins.
• Incorporate processes that can alter their operations on demand.
• Incorporate ways to isolate infrastructure from wildfires during peak effects.
• Plan for contaminants that are regulated as hazardous to public health
• Add additional phases of treatment for fine particulates.
• Develop automated valving systems that operate based on water quality monitoring results.
• To reduce dependency on grid electricity:
  • Reconfigure backup power systems to last for duration of fires, i.e., days instead of hours.
  • Install solar panels.
  • Use backup batteries and generators with automatic transfer switches.
  • Install large-volume, fuel storage tanks with propane instead of diesel.

Mitigate risk through material changes:

• Use concrete masonry unit structures, metal roofing, and smaller roof eaves.
• Use heat-resistant pipes such as metal pipes.
• Construct water storage tanks and other vulnerable infrastructure out of fire-resistant materials.
• When upgrading facilities, incorporate design elements from the section, “Eliminate Risk through Design.”

Lower risk through maintenance:

• Test water quality more frequently.
• After a wildfire, evaluate whether infrastructure needs replacement; e.g., plastic pipe may appear serviceable, but previously heated plastic can continue to leach chemicals into water supplies.
• Stabilize pipes using in-situ technology such as cured-in-place piping and pipe bursting.
• Clear potentially fire-spreading vegetation to 200 feet around facilities.
• Use sprinklers to increase soil moisture.
• Remove trees and fire-prone invasive species that could touch or fall on power lines.

Evaluate how well you can manage risk through operations by asking these key questions:

• Will you be able to continue operations during a power loss resulting from a wildfire?
• Is there adequate filtration and treatment for fine-grained sediment introduced to waters during and after wildfires?
• Are you prepared to replace distribution system infrastructure after a wildfire?
• Do you maintain your treatment plant to reduce impacts should a wildfire pass through the area?

Resources for the Next Step

Identifying risk factors is the first and foremost step for mitigating the damage wildfires cause to water systems. Although assessing a water system and taking measures to reduce the risk of wildfire damage can be difficult and expensive, multiple government and university-funded programs offer free online resources to help. Here are some examples:

• U.S. Geological Survey fire risk, large fire probability, and fire spread probability seven-day projection for the United States

• U.S. Department of Agriculture prescribed fire training exchanges

• U.S. Environmental Protection Agency’s searchable chemical database

• Data maps for wildfires and air quality

• Bureau of Indian Affairs, Branch of Tribal Climate Resilience

• “Private Wells After a Wildfire,” Centers for Disease Control and Prevention

A Huge, but Local, Problem

The U.S. government manages about 640 million acres of public land. That’s 28 percent of the nation’s total land area. Many federal departments and agencies manage drinking water sources such as reservoirs. The risk of wildfire on federal lands—and resulting impacts on water quality—is high. Between 2018 and 2021, 24 million acres of federal lands and more than 14 million acres of nonfederal lands burned from wildfires, so understanding this issue is critical for national parks and public land managers.

Large public water systems have the resources to make operational adjustments to minimize the threat to water quality from wildfires. But smaller, simpler systems, typically supplying water to fewer than 10,000 people, are less capable of adjusting to changes in water quality. Nevertheless, some of the solutions we suggest apply to those smaller systems as well. Without evaluating the risks and having adequate compensatory mechanisms, the damage from wildfires may pose a serious threat to the health of the communities those smaller systems serve. The scope of the problem is huge: smaller systems account for 97 percent of public water systems in the United States.

We can’t eliminate wildfires on public lands, nor would that be wise. Fire is essential to the health of our native landscapes, particularly in the West. But climate change has disrupted the natural cycle of wildland fires, and they are now more frequent and severe. More frequent and severe wildfires increase the urgency of reducing risks to drinking water sources and distribution systems, which provide vital ecological and social services. Impacts from wildfires complicate the water treatment process and can endanger public health. Not knowing the full extent of wildfire’s impacts on water sources and infrastructure is also a hindrance, and some “burning” questions remain.

Further Questions to Answer

• What are the synergistic impacts of contaminants on water quality?
• What are best management practices for water treatment mitigations in high-risk wildfire zones?
• What effect do wildfires have on aerosolized transport of living things, including bacteria, fungi and their metabolic products?
• How do wildfires affect roads and bridges?
• What are the public health impacts from wildfires?
• How do wildfires affect people in residential spaces and hospitals?

Protecting public drinking water sources from the impacts of increasingly hot and frequent wildfires brought about by climate change is one of our greatest challenges. Knowing how to do it will require dedicated scientific research and careful management.

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About the authors

^{LCDR Michael Wandersee is a project engineer for Interior Regions 5 and 7 of the U.S. Fish and Wildlife Service. Image courtesy of Michael Wandersee.}

^{LCDR Dara Zimmerman is a project engineer for Interior Regions 9, 10, and 11 of the U.S. Fish and Wildlife Service. Image courtesy of Dara Zimmerman.}

^{LCDR Kelly Kachurak is branch manager of the National Park Service’s Sustainability, Environmental, and Accessibility Program Branch, Southeast Regional Office. Image courtesy of Kelly Kachurak.}

^{CAPT Leo Angelo Gumapas is chief of the Environmental Engineering Program at the U.S. Public Health Service, Department of Health and Human Services. Image courtesy of Leo Angelo Gumapas.}

^{LT Kayla DeVault Wendt is a project engineer for Interior Region 8 of the National Park Service. Image courtesy of Kayla DeVault Wendt.}

^{CAPT Kurt Kesteloot is the supervisory public health consultant for Interior Regions 3, 4, and 5 of the National Park Service. Image courtesy of Kurt Kesteloot.}