Two months after a wildfire burned through Paradise, Calif., in 2018, Kevin Phillips, then a manager for the town’s irrigation district, walked from one destroyed home to another.

“You started to actually be shocked when you saw a standing structure,” he said.

Phillips, now town manager, was following the team taking samples from intact water meters connected to homes that were now reduced to gray ash. He knew from the Tubbs Fire in 2017 that toxic chemicals were very likely to be in the water distribution system: Rapid action would be needed to protect people returning to the community from the dangers of substances like benzene, which can cause nausea and vomiting in the short term, or even cancer over time.

Wildfires this year are increasingly engulfing people’s homes, continuing to rage in California, Colorado, Oregon and Washington. But even when homes don’t burn, other dangers arise in the aftermath, and experts are focusing more attention on what happens to municipal water systems after a fire, when released toxic chemicals can get pulled into plumbing systems, and other damage can linger in pipes for years.

After the fire that destroyed Paradise, for example, tests reported in a new study showed benzene levels in drinking water at 2,217 parts per billion. The Tubbs Fire led to levels as high as 40,000 parts per billion. California authorities say 1 part per billion is dangerous over the long term, and 26 parts per billion is dangerous for short-term exposure. And many other compounds that end up in water after a fire can also create health risks.

Angela Aurelia and other residents of Boulder Creek in Santa Cruz County say they are following guidelines that are not devised for this kind of disaster.

After a fire, water in houses and in the underlying pipes “can become contaminated with an array of volatile organic compounds and semivolatile organic compounds” at levels that exceed the regulatory limits set, said Amisha Shah, a water quality engineer at Purdue University.

Volatile organic compounds, such as benzene, naphthalene and methylene chloride, have a low boiling point and can be dispersed into the air easily. Semivolatiles, including chrysene and benzo (b) fluoranthene, have a higher boiling point but can be dispersed during, for example, a warm shower. Although not all of these compounds are harmful, some have been found to cause cancer in the long term.

Shah was a co-author of the study published by AWWA Water Science that summarized the lessons from the past few years. Analyzing sample data from the Tubbs Fire as well as the Camp Fire that destroyed Paradise, the researchers found some of those harmful chemicals caused by wildfires throughout the distribution system.

The researchers’ observations lined up with Phillips’ experience in Paradise two years ago. “Over 50% of those service lines from burned structures had some detection of contamination,” he said.

But he noticed there was a randomness to it. Water in one house would be contaminated, while the neighboring system would be clear.

How water moves through distribution systems, especially during a wildfire, is complex and needs more study. But researchers say that a loss in pressure, which occurs when fires damage pipes, turns the plumbing into a vacuum that sucks smoke and other toxic chemicals out of burning homes. Those substances then get circulated throughout a community’s water distribution system.