How Climate Change Puts the Safety of Drinking Water at Risk

How Climate Change Puts the Safety of Drinking Water at Risk

On November 8, 2018, a power line dropped into dry grass in the foothills of the Sierra Nevada mountains, north of Sacramento, and ignited the deadliest fire in California’s history. Powerful winds swept flames through Paradise and several other small towns in the tinder-dry forest, killing 85 people, destroying 18,000 structures, and causing more than $16 billion in damage.

Among the fire victims was the city’s water system, poisoned by the toxins in smoke. “Every time a home burns, it’s an open line to the atmosphere,” said Kevin Phillips, a former town manager and the district manager for the Paradise Irrigation District, which provides drinking water to more than 9,000 customers. “You are squirting water out [of lines that supply homes] at full speed and eventually [the system] depressurizes. That creates a vacuum effect and sucks in smoke with contaminants back into the system.” Smoke from burning trees, plastics — including PVC water pipes — and other materials contain benzene and other carcinogens. A year after the fire, testing revealed levels of benzene 80 times higher than the legal limit in some drinking water samples.

The road back to a healthy water supply has been long, requiring many rounds of flushing the system, testing, and replacing pipes. But this August, after seven years of work and expenditures of $40 million, the town’s new water system will be finished and all toxic substances flushed.

Flooding in Asheville washed away large water pipes and damaged backup pipes buried 25 feet underground.


From fires to floods, droughts, extreme heat, and sea level rise, climate change is taking a growing and serious toll on drinking water supplies around the world. The changes hit hardest in places with already stressed, or fragile, municipal water systems. And as such climate impacts worsen, they are forcing expensive fixes — if fixes exist at all.
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“Climate change is having a significant impact on the availability of our water resources from a quality and quantity perspective,” said Alexandra Campbell Ferrari, executive director of the Center for Water Security and Cooperation. “We are not really addressing the challenges. Ultimately, we’ll be unprepared to address the floods and drought and pollution that we will continue to be faced with.”

More than half of the U.S. population drinks water that’s captured and filtered by forested lands. But with wildland fires growing in intensity, frequency, and duration, surface water supplies in those watersheds are increasingly contaminated with dissolved carbon, heavy metals, and excessive nutrients, including nitrogen and phosphorous, from burning trees and other forest materials. When fires burn houses and towns, plastic pipes and other human-made materials pollute the water system. And after the fires, mudslides often occur, washing sediment, debris, and other contaminants into surface water, compounding water quality problems.



A home burns in the 2018 Camp Fire in Paradise, California. When houses burn, plastic pipes and other human-made materials pollute the water system. Justin Sullivan / Getty Images


Flooding poses a major threat to drinking water systems worldwide as the climate warms and the atmosphere holds ever more moisture. Last September, Hurricane Helene swept up the U.S. East Coast, dropping 14 inches of rain on Asheville, North Carolina, over the course of three days. The once-in-a-thousand-year deluge wiped out homes, businesses, and infrastructure in the mountain community — including the city’s water system.

The flooding washed away the large-diameter pipes that carried water from treatment plants to the rest of the system and damaged back-up pipes buried 25 feet underground. The 1,000 miles of smaller pipes in Asheville that carried water to businesses and residences were also heavily damaged.

This wreckage was even more striking because it happened to a system built in 2004, which was designed to be more resilient in the wake of a previous flood event. Officials “thought they were building the best they could with the means they had at the time,” Asheville Mayor Esther Manheimer told The New York Times last year. “I don’t know how you can build a system that can withstand a 1,000-year flood situation like we just experienced. If you had all the money in the world, you probably could. When you’re a city on a budget of $250 million a year, you know, you can’t.”

“Wastewater systems are not designed for this changing climate. They were designed for an older climate that doesn’t exist anymore.”


The problem is worse in countries without, or with minimal, water infrastructure. Recent extreme flooding events in Pakistan, Niger, and Chad flooded sewers and latrines. Pathogens were washed into drinking water, which resulted in outbreaks of diarrhea and cholera. In Chad, which was already suffering from a food crisis, contaminated floodwaters also destroyed stores of food as well as crops in fields. In southern Brazil, flooding in the spring of 2024 contributed to an increase in leptospirosis in urban settings with inadequate sanitation systems.

High-intensity rain storms can also wash toxic chemicals from fertilized fields, industrial sites, and roads into streams and reservoirs. The contaminants complicate the water-treatment process as systems overflow, equipment breaks down, filters clog, and more disinfectant is required. Because many sewage and water treatment plants are built along streams and low-lying areas prone to flooding, as in Asheville, climate change is expected to damage more of these facilities. Such challenges increase the risk of contamination both immediately and over the long term.

“Wastewater systems are not designed for this changing climate,” said Sri Vedachalam. “They were designed for an older climate that probably doesn’t exist anymore.”



A "boil water" advisory set up in Old Fort, North Carolina, after Hurricane Helene flooded the local water treatment plant last October. Robert Willett / The News & Observer via AP


Wells are at risk too. Testing after Hurricane Helene showed that E. coli and coliform bacteria contaminated 40 percent of the private wells in the path of Helene. Studies have shown that flooding and heavy rains can cause human feces and other contaminants from leaky septic systems to seep into public and private wells. Some 53 million people in the United States rely on private wells, which are not regulated by the federal government and are not subject to mandatory treatment for contaminants.

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Droughts — made more frequent and intense by climate change — can also affect water quality. When water levels are low, organic material, such as decomposing leaves and other vegetation, gets concentrated in surface water sources, which spurs treatment plants to use more disinfectant — typically chlorine. But organic material can react with chlorine to create two families of toxic disinfection byproducts (DBP) — trihalomethanes and haloacetic acids. Utilities face a balancing act: Using too little chlorine could allow opportunistic pathogens to survive. Using too much chlorine could allow harmful DBPs to build up in drinking water. A recent analysis found some evidence that trihalomethanes, even at levels below regulatory limits in the U.S. and the European Union, increase the risk of bladder and colorectal cancer over decades of consumption; haloacetic acids are also considered a potential carcinogen.

In Mozambique, drought has led to a lack of clean water, leading to an increase in water-borne diseases like cholera.


Globally, rural areas that lack advanced water treatment systems also suffer. In Mozambique’s Nampula Province, climate-related drought has diminished rivers, shallow boreholes, and wells; the lack of clean water has contributed to rising cases of tropical diseases like scabies, schistosomiasis, and lymphatic filariasis, according to Doctors Without Borders, in addition to water-borne diseases like cholera and diarrhea. A solution: digging deeper and better-covered wells.

Fertilizer runoff and contaminated stormwater from extreme rainfall, combined with warmer water temperatures, are also increasing the frequency and intensity of harmful algal blooms in freshwater. After a massive algal bloom occurred in Lake Erie in the summer of 2014, residents of Toledo, Ohio, were warned not to drink their tap water because it contained cyanotoxins generated by thick green slicks of algae. Exposure to these naturally occurring compounds, through swimming in or drinking affected water, can cause serious illness and even death.

Experts say the risk of algal blooms, and their risk to drinking water, is growing. Lake Erie’s “blooms are starting earlier,” said Sean Corson, director of NOAA’s National Center for Coastal Ocean Science told Inside Climate News. “They’re lasting longer. Their peaks are larger. So, by some measures, they’re getting worse.”



A glass of water collected from Lake Erie during an algae bloom in July 2015. Eric Albrecht / The Columbus Dispatch via AP


Ocean water is also threatening drinking water supplies as river volumes decline. The Mississippi River has experienced a drought over the last two years, due to lack of precipitation and excessive heat. The low river levels have allowed saltwater to travel from the Gulf of Mexico further upstream, threatening to contaminate New Orleans’ drinking water.

“Lately it’s been an extremely low river,” said Mark “Hobbo” Cognevich, who works on water issues as a district representative for Plaquemines Parish, at the mouth of the Mississippi. “The seawater is rising and so it’s moving its way upriver against the freshwater coming down.” Saltwater intrusion has become more frequent in the last few years, said Cognevich. Last year, parish officials delivered bottled water to residents, and the utility occasionally trucks in reverse osmosis filters, or desalination units, to supplement its water treatment until a new plant in Belle Chasse with reverse osmosis capabilities can be completed.

To cope with the growing risk of fires to its water system, Paradise, California has learned hard lessons on how to prepare.


Utilities across the U.S. are working on various fronts to adapt to the changing water picture. In Paradise, to cope with the growing risk of fires, Phillips said the city has learned hard lessons on how to better prepare. “We put in concrete meter boxes everywhere so they are more resilient to heat,” he said. “We use brass meters, no more plastic meters. And every house is equipped with a backflow device, so if a house was to burn down there would no longer be the opportunity for a vacuum effect.”

According to a recent report by the Pacific Institute, the Center for Water Security and Cooperation, and DigDeep, which promotes clean-water initiatives in underserved communities, a key part of adapting to climate impacts on water systems is legal reform.

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“Until our laws reflect some kind of instruction manual that says we need to think about how we are managing our water resources” — including protecting minimum stream flows and aquifer levels, reducing the amount of pollution going into water, and prioritizing equitable access to drinking water — “we aren’t going to achieve those goals,” said Ferrari, of the Center for Water Security and Cooperation. “The law creates the impetus for change.”