Even as bushfires push into new swaths of Australia, the communities close to and within the nearly 30 million acres that have already burned are starting to reckon with a complex, expensive aftermath: fire's threat to their drinking water.

It's a vexing problem that a growing number of people around the world have had to cope with over the last two decades, as climate change fuels hotter, bigger fires that destroy forested catchments and consume towns and their water systems, engineers and scientists said.

More than a year after a 2016 wildfire turned into the costliest disaster in Canadian history, Fort McMurray, Alberta allocated hundreds of thousands of dollars in additional funding to remove ash from drinking water sources. In 2017, the Tubbs Fire damaged the water distribution system in part of Santa Rosa, California. A year later, the enormous, deadly Camp Fire led to widespread chemical contamination of the water infrastructure in Paradise, California.

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Wildfire poses layers of risk to drinking water that unspool over time and geography, with some effects emerging years later, sometimes outside the burn zone, depending on where waterways take the pollutants. Water utility managers, engineers and scientists have only recently begun to grapple with the aftereffects of fires that consume entire neighborhoods and towns—as they did in California—and that in the process, release dozens of manmade pollutants into water lines. As climate change increases the risk of wildfire and more communities encroach upon fire-prone zones, the threat to drinking water promises to grow.

"Wildfire is going to affect water," said Monica Emelko, director of the Water Science, Technology & Policy group at the University of Waterloo in Ontario. "And it's going to cost, and it's going to be bad."

Often, the immediate concern among government officials after a wildfire is that bacteria has gotten into the water. Authorities issue boil water advisories, secure alternative sources of water if they can, such as trucking water in, and tell people to use bottled water.

Bushfires that decimated half of Kangaroo Island in the state of South Australia destroyed part of a water treatment plant, rendering it inoperable for almost three weeks and sending utility officials scrambling to protect residents and find alternative water sources.

Yet larger problems loom. Australian water managers have dealt with bushfire before, but the challenge now is the vastness of the damage from this fire season, said Erin Cini, liveable communities manager at the Water Services Association of Australia, an industry group. Most of the country's population lives in the southeast, and almost every water utility there now faces the effects of the bushfires, she said.

"You won't find Australian water professionals denying climate change," Cini said.

Some of her group's members have had several bushfires burn through their watershed in the last few years.

"If this is the new normal, where we're likely to see an increase in bushfires and longer seasons, then the water industry will keep learning and investing in preparedness," she said.

The most heavily populated parts of Australia get their water from rainwater draining through forest catchments that have been "severely and extensively damaged," said Stuart Khan, a professor in the School of Civil and Environmental Engineering at the University of New South Wales. Some fires have been burning since October, and water managers have to safely make their way to catchment areas to assess the risk their treatment facilities will ultimately face.

The more intense the burn within the catchment, the greater the run-off will be, Cini said. If the damage is on steep slopes, that also worsens run-off. Ash, trees, animal carcasses and other pollutants left by the bushfires can flow into dammed reservoirs that supply drinking water to communities. And the loss of vegetation means that watershed soils are less stable and prone to erosion into waterways, Khan said.

Sydney, a city of 5.2 million people, draws around 80 percent of its water from a reservoir called the Warragamba Dam. About 30 percent of the sprawling catchment area for the dam has burned, Cini said. Extremely heavy rains in the area this weekend flushed the first serious wave of debris and sediment into water sources, increasing the turbidity of water in some places. Water utilities have responded "by installing sediment control in the catchments and reservoirs," dosing water with powdered activated carbon and using other water sources instead, Cini said.

Heavy rainfall over the weekend in Sydney, Australia, deluged a year’s worth of water into the city’s main water reservoir, the Warragamba Dam, in just two days. Credit: Jenny Evans/Getty Images

Like water utilities wherever bushfire has spread, the New South Wales authorities have set up barriers along tributaries to their reservoir to catch big debris such as trees, and silt curtains at the dam to reduce sediment entering the treatment process.

Water treatment facilities are used to dealing with sediment. But wildfires create such large amounts of debris run-off that water managers use barriers and silt curtains to slow the flow into treatment centers so that they can handle the volume. Treatment systems clog more frequently because of increased debris, which slows down water purification. "If we have a lot of sediment come through, then we spend lots of time backwashing and less time providing drinking water, which can lead to shortages," Khan said.

Ash run-off can also have longer lasting effects on drinking water sources which are not immediately evident. When vegetation burns, phosphorus and nitrogen end up in the ash, which then runs off into waterways. The excess phosphorus and nitrogen can then spur algal blooms and cyanobacteria growth in bodies of water months—or even years—later, sometimes far from the burned areas.

Cyanobacteria, or blue-green algae, make water smell terrible, and they can produce toxins such as microcystin, whose presence in Toledo, Ohio's drinking water in 2014 led to a temporary shutdown of the city's water supply. Chlorine used in water treatment can break down cyanobacteria, but the bacteria's proliferation in waterways still poses a threat to pets, livestock and wildlife.

"Once it's in the water, there's not a lot you can do to the water body itself," Khan said. But "you can adjust where you get the water from, you can get it deeper than you usually would from the surface of water storage."

Cini estimated that water utilities could be grappling with the effects of the bushfires, including algal blooms, for up to three years.

Water containing extra sediment, substances and nutrients from wildfires can be effectively treated, but it's difficult and expensive for many communities whose water treatment systems were not built for such emergencies. Emelko and Uldis Silins, professor of agricultural life and environmental sciences at the University of Alberta, have researched the impact of wildfire on water for 16 years. But in the last five or 10 years, demand for their expertise has skyrocketed, including in May 2016, when a wildfire swept into Fort McMurray, a hub of tar sands mining in Alberta.

Concerned from the outset about protecting drinking water, local officials asked Emelko and Silins to join the disaster response team immediately. The researchers have seen the toll the fire took on Fort McMurray's water treatment. The local water utility spent hundreds of thousands of additional funds two years after the fire to rid it of ash.

Emelko was concerned that along with the sediment and nutrients, more dissolved organic carbon was in the water, which can make it harder to treat. Those challenges could ultimately lead to shortages and service disruptions, said Emelko, who is also a professor in the department of civil and environmental engineering at the University of Waterloo.

Cost often becomes a burden. "Fort McMurray spent millions on it, and the effects are still playing out," she said. "We can make water safe to drink in the Space Station, so it's possible to make safe drinking water. The question is: how much do you want to pay for it?"

Scientists and engineers have far less experience dealing with manmade pollutants that make their way into water after fires race through communities. Australia so far has not begun to tackle the issue, but the bushfires have already destroyed more than 2,000 structures in New South Wales alone.

Even when fire damages water mains, service lines, meters, pipes, irrigation systems and private wells, people haven't typically paid attention to the chemical contamination that could occur, said Andrew Whelton, associate professor at the School of Environmental and Ecological Engineering at Purdue University.

Fire that rips through a community incinerates, among other things, metal, vinyl siding, tires, the plastics and chemicals in buildings, much of which ends up as particulate matter and gases. Some plastics in the water distribution system burn up, too, a process known as thermal decomposition.

In the United States, the 2017 Tubbs Fire in northern California heightened awareness of the risks. About a month after the fire, the city of Santa Rosa got a complaint about an odor in the drinking water. Tests revealed the presence of volatile organic compounds (VOCs) in the water, including the carcinogen benzene at levels greater than state and federal limits. The city determined that the water at the treatment plant was safe, but that chemical contamination had occurred in the distribution system, including pipes, meters and valves, Whelton said.

VOCs and other chemicals can enter municipal water in several ways. When structures burn, the meters and plumbing which link them to the municipal water system also burn, creating a leak in the water system at the site. The pressure in water lines and mains drops as a result of the multiple leaks in the distribution system, "like your circulatory system bleeding out," Whelton said. The leaks create a vacuum that pulls in air and delivers the aerosolized pollutants to whatever water remains in the pipes, or deposits them in dry pipes, where they can contaminate clean water when it's pumped back in. Regular testing revealed that the contamination affected only a small section of Santa Rosa, and it cost, in the end, about $8 million to remediate.

A year later, the massive destruction of the Camp Fire considerably elevated the threat of chemical contamination. The deadliest wildfire in California history, the 2018 Camp Fire killed 85 people and destroyed about 18,000 buildings, including virtually the entire town of Paradise. The fire affected 13 water systems, with the Paradise Irrigation District (PID) being the largest.

Possible contamination was already on the minds of PID officials because they had followed what had occurred in Santa Rosa, said Kevin Phillips, PID's general manager. Tanks that held water in the town were empty, in part because 9,000 homes had burned, creating a massive leak and loss of pressure. Still, about 1,500 homes remained, and people would be returning to them, PID knew.

The water managers issued warnings not to drink or boil the water—boiling could worsen exposure to VOCs. PID worked with Whelton and a team from Purdue and Manhattan College in Riverdale, New York to identify and remediate the contamination. Testing revealed that the water at the reservoirs that fed the town was fine. But tests within the distribution system of water mains, pipes and individual service lines to buildings showed the presence of toxic substances, including benzene, methylene chloride, xylene and styrene, Phillips said.

The Paradise water system is made up of 173 miles of pipes, not including the individual service lines to each building, which are about 35 feet long each. To date, nearly 160 miles of pipe and 983 of the 1,556 service lines to intact structures have been cleared of contamination. Anyone who rebuilds will get a new service line, Phillips said.

"It's going to be a long process," he said, adding, "Our big goal is to bring trust back to the water system."

Residents who returned to intact homes still have questions about whether the plumbing inside is contaminated. The Camp Fire exposed houses to extreme heat, melting the stucco on some, Phillips said. It remains unclear what kind of impact the heat had on plastic plumbing just inside the walls.

Analyzing in-home water quality is the responsibility of homeowners, and every week, Whelton said, homeowners email him asking how they should test their water and how they can be assured that it's safe.

"There needs to be a methodical procedure for warning the public about unsafe water after a wildfire and testing to rapidly determine if it is safe or unsafe," Whelton said. "Water utilities are not used to disaster recovery. They're not used to exotic contamination of their system. It's pretty specialized. State and local officials don't have the expertise for this. They don't want to face unknowns with as much uncertainty as they did. They want to do the right thing and they don't have the resources for that."

Phillips began paying attention to the Australian bushfires early, a reflex he's developed now whenever news of wildfire spreads. He is following how many structures have burned, and one of PID's engineers reached out to Australian colleagues, offering assistance, but has not gotten a response yet.

"We're definitely there to help with the next disaster," Phillips said, "because we know we won't be the last. We just want to help make recovery go faster than it has."