At least seven water districts in Los Angeles County — five in the Altadena area and two in the Malibu/Palisades area — have issued do-not-use or do-not-drink water advisories since the Eaton and Palisades fires began burning earlier this month, meaning customers should not use that water until they get the all-clear.

If you’re wondering how fires can make drinking water dangerous, the first thing to understand is this: The structures where we work and shop, dine and sleep and just generally live our lives are full of materials that release toxic waste when those materials burn.

The examples are numerous. Couches and mattresses, TVs and refrigerators, tires and toys, even clothes are full of polyurethane and plastics, which vaporize into a toxic smoke once they’re set on fire, said Dr. Gina Solomon, chief of the Division of Occupational, Environmental and Climate Medicine at UC San Francisco.

These toxins — many of which are known as VOCs, or volatile organic compounds — include chemicals such as benzene, which is used to make just about everything in the modern world, from plastics and gasoline to detergents and pesticides. As a liquid or vapor, though, benzene is a carcinogen if ingested or inhaled. Longtime exposure damages bone marrow, which is why it’s linked to leukemia.

Most studies about benzene are based on many years of exposure, Solomon said. “What a few months does, nobody knows exactly, but nobody wants to find out,” she said. “We don’t want to use the population of burn zones to see what months or weeks of exposure does. We want to just avoid exposure in those areas.”

How can these toxins get into water systems?

If a water system loses water pressure, that allows contaminants such as bacteria and vaporized VOCs and other toxic chemicals to get inside, Solomon said.

“Normally our water systems have positive pressure — they’re full of water, so nothing can get in the pipes,” she said. But if the pipes lose pressure, such as water hydrants running dry, “It can create situations where you get suction instead of pressure, and in this case, it’s not a backflow of [contaminated] water but air full of toxic chemicals, including VOCs.”

Solomon studied this phenomenon after the Camp fire destroyed about 18,000 structures in the Northern California town of Paradise in November 2018. In a second study, “Organic Chemical Contaminants in Water System Infrastructure Following Wildfire,” she and other researchers identified 95 contaminants in water systems that came not just from melted pipes but also from “the intrusion of smoke” after the Camp fire in Paradise and the 2017 Tubbs fire in Santa Rosa.

A home on El Medio Avenue in Pacific Palisades burns on the night of Jan. 7 during the Palisades fire.

(Brian van der Brug / Los Angeles Times)

Only one neighborhood in Santa Rosa — Fountain Grove — lost water pressure during the Tubbs fire, Solomon said. The hydrants there ran dry, and the water to the neighborhood’s surviving 13 homes developed a contamination problem. Residents reported that their water smelled like gasoline, she said, and testing revealed benzene contamination for reasons investigators couldn’t explain.

“That was our first hint,” Solomon said. Researchers didn’t really understand what was happening, however, until after they were able to do more extensive testing on the drinking water for the 1,200 surviving homes in Paradise. That’s when they learned that VOCs and other contaminants could enter the drinking water even in a smoke or gas form if the water systems lost pressure.

As a result of their findings, the state Assembly passed a new law, California Health and Safety Code Section 116596, that went into effect Jan. 1, 2024, mandating that if a structure or structures burn in a wildfire of 300 acres or more, water districts must test their water and deem it free of contaminants before it can be used by customers.

“So basically we are guilty until proven innocent, based on this law,” said Tom Majich, general manager of the Kinneloa Irrigation District, the smallest of the five water districts in the Altadena area with water advisories. “And I’m not saying that’s wrong. Some of us may be guilty, but I just want people to understand that putting out a [water advisory] notice doesn’t mean you have a problem. We’re just following the law.”

Majich is awaiting his district’s test results, and he’s hopeful his system will be deemed safe. The district’s water system did not lose pressure, he said, and less than 7% of the district’s 600 customers — roughly 40 structures — were burned in the fire. “My personal opinion is that our water system was not compromised, but the law says that doesn’t matter,” Majich said. “If you lose a house, you do the testing, so we’re waiting for the results.”

The other Altadena-area districts with water advisories are Las Flores Water Co., Lincoln Avenue Water Co., Pasadena Water and Power (in the northeastern part of the district) and Rubio Cañon Land & Water Assn. Water advisories also have been issued by Los Angeles Department of Water & Power for the Palisades area and for Los Angeles County Waterworks District 29 in Malibu.

Majich said he doesn’t know when his district’s test results will be in. He speculated that other water districts haven’t had a chance to test yet because their offices and systems were so badly damaged in the fire. “They’re still really in crisis mode,” he said. Calls to the other districts for comment were not returned.

Why can’t you boil your suspect water?

Boiling can eliminate bacteria, another concern in contaminated water systems. What’s dangerous is when the water is full of volatile organic compounds, Solomon said, because “when you boil the water, it releases benzene and other chemicals into your kitchen.”

Hot showers or baths can vaporize those chemicals too, and if there’s bacteria in the water, it could splash in your eyes, nose or mouth. That’s why most of the water advisories have do-not-use alerts until the systems can be thoroughly tested, repaired and cleaned.

A gutted washer and dryer are among the ashy remains of a home destroyed by the Eaton fire on Wapello Street in Altadena.

(Ringo Chiu / For The Times)

Sometimes the closures are just precautionary, Solomon said, and can be quickly resolved once officials determine that water is safe. But in Paradise, several systems had to be repeatedly flushed because most water pipes are coated on the inside with biofilm, microorganisms that attach to surfaces “that absorb and hold on to all the toxic chemicals,” she said.

“Once the biofilm is contaminated, it’s difficult to get those chemicals back out of the pipes. In Paradise, they had to flush the entire water system seven times, and some of those service lines [between water mains and houses] were so contaminated they had to go in and dig them up and just replace them,” Solomon said. “So basically what we saw in Paradise was about a six-month process, and I think we can anticipate a similar time frame in the most impacted parts of L.A.”

Once a water system gets the all-clear, people should feel confident about the quality of their drinking water, Solomon said. “I know a lot of people will be fearful, and may not trust the results, but I have great faith in the actual testing data,” she said. “Once they’ve done the testing, and the area is negative [for contaminants], it means people can breathe a sigh of relief that they’re not in an area impacted by water hazard.”

A smoky haze fills the dusk landscape as a home smolders in the foreground during the Eaton fire in Altadena on Jan. 8.

(Gina Ferazzi / Los Angeles Times)

Can you do anything safely with suspect water?

Basically, Solomon said, water with suspected contaminants should be avoided.

That means:

• No bathing or showering in the water (even cold showers could be dangerous if the water gets in your eyes, nose or mouth).
• No cooking or making ice.
• No teeth brushing.
• No washing dishes (since hot or warm water could release the toxins).
• Pets should not drink the water either.

Solomon said she’s not sure how watering plants outside would be affected. VOCs would evaporate in sunlight, she said, but there hasn’t been much research on what other potential contaminants could do.

The safest course, she said, is to just not use the water until it’s deemed safe.

Vegetables, fruits and plants growing outdoors shouldn’t be adversely affected by the water either, she said. The bigger concern outdoors is stirring up the ash from burned-up structures, which is also full of toxins, Solomon said, so be sure to wear gloves and an N95 mask to avoid inhaling the ash.