As fires continue to burn across Los Angeles, several utilities have declared their drinking water unsafe until extensive testing can prove otherwise.
A warmer, drier climate means wildfires are getting worse, and encroaching on cities — with devastating impact. Toxic chemicals from those burns can get into damaged drinking water systems, and even filtering or boiling won’t help, experts say.
Last week, Pasadena Water and Power issued a “Do Not Drink” notice to about a third of its customers for the first time since it began distributing water more than a century ago. With at least one burned pump, several damaged storage tanks, and burned homes, they knew there was a chance toxic chemicals had entered their pipes.
“Out of the abundance of caution, you kind of have to assume the worst,” said Stacie Takeguchi, chief assistant general manager for the utility.
This week, they lifted the notice for most of the area after testing.
Why urban fires are a risk to drinking water
When large fires burn in towns and cities, rather than forests and grasslands, infrastructure can be heavily damaged. When drinking water systems are damaged in a fire, “we can have ash, smoke, soot, other debris and gases get sucked into the water piping network,” said Andrew Whelton, a Purdue University engineering professor who researches water contamination in communities hit by fire.
Those elements can be particularly toxic because chemically engineered synthetics in building materials and households are heating, burning and releasing particles and gases, he said. Some of those chemicals are harmful even at low concentrations, experts say.
How chemicals get into the pipes
Water systems typically are under enough internal pressure to keep harmful elements out. But that critical pressure can be lost in many ways during a fire, which means toxins can get in.
There’s normal demand on the water system from people who didn’t need to evacuate. Firefighters use a lot of water. Pipes in burned buildings can be damaged, spewing water.
Power loss can also cause pressure loss when pumps stop working, said Greg Pierce, professor of urban environmental policy at the University of California. This happened during the 2023 Maui fires.
“It’s really hard, if not impossible, to keep up the power supply to the whole water system in the event of a fire, because you’re either shutting off the power, because power can contribute to the fire, or it just goes out,” Pierce said. “And then you’re relying on generators at best in spots.”
The loss of pressure can affect not only water quality but also water availability for firefighting. Hydrants ran dry in the Pacific Palisades neighborhood as surrounding homes burned. The utility says it was from high demand and the pumps were working, but California Gov. Gavin Newsom said the state will investigate.
What’s the health risk?
