Depressurization, another major contributor to contamination, occurs when firefighting efforts draw massive amounts of water from the system in a short period of time. “The water line that connects to the house can generally put out about 9 gallons per minute,” says Whelton. “Firefighters can pump out 500 gallons or up to 1,500 gallons of water per minute. So if you were to run five or six truckloads of pumps from the water line, you would be looking at thousands of gallons of water being pulled out of the water system in a very short period of time.”
When this happens, the water pressure drops sharply, and the system becomes susceptible to bacteria or chemicals entering the system from the surrounding environment. Typically, the high water pressure within the system prevents any external contaminants – such as soil or groundwater – from finding their way inside the system components.
Structural fire damage can also result in pressure losses, Whelton says. In the event of a large-scale fire such as the Palisades or Eaton fires, you can have massive amounts of water released uncontrollably from the system, due to burst pipes and other parts of the system. Where there is damage, smoke and debris can be drawn into the plumbing system, while damaged sewer lines can leak into nearby drinking water pipes. “When the water utility starts trying to repressurize, it starts pushing that contaminated water through the infrastructure again,” Whelton says.
During the 2021 Marshall Fire in Louisville, Colorado, which burned more than 1,000 homes, city officials advised residents to use tap water only for flushing until extensive testing confirmed its safety. With more than 12,000 buildings burned in Los Angeles as of Monday morning, the potential for widespread contamination is significant, Kearns warned.
The coming days and weeks will be crucial. After water experts assess the damage, they will determine if the system can be flushed or if infrastructure repairs are needed. If enough is burned, workers will have to replace pumps, pipes and even tanks. For parts of Los Angeles County served by LADWP, McCurry estimates recovery could take anywhere from days to weeks.
Altadena and the surrounding areas, however, are served by several smaller water suppliers, such as Lincoln Avenue Water Company, Las Flores water company, Rubio Canon Land and Water Associationand Kinnelo Irrigation Area—all issued Do Not Drink notices. “In the case of a large water system like LADWP, you’re probably going to see things continue a little faster,” Kearns says. “Smaller water suppliers, who may sometimes only have a few employees and don’t have the budget for events like this, can struggle.” Santa Cruz experienced similar challenges during the 2020 CZU Lightning Complex fire, with water supplies taking months to stabilize. McCurry warns that some regions could take years to rebuild or overhaul large systems that burned down.
It’s critical for residents to stay informed about recovery efforts, as alert systems can be complicated, and many residents may not even receive them, Kearns says. People should “proactively look for any boil or Do Not Drink warnings from your water supplier, your city, your county,” she advises. “Share them with your neighbors and make sure all people whose first language is a language other than English get those warnings and understand what’s going on.”
Some places, like Louisville, Colorado, and Maui, Hawaii, have released public access maps that track water quality on each parcel of land, helping to inform residents in the months and years that followed.
Before the warning was lifted, the state of California legally required water suppliers to monitor for benzene. However, Whelton cautions that benzene is not the only chemical of concern and that the list of potential contaminants is long. Government agencies and third-party testing services do not always account for every possible exposure. “It’s possible that some of these chemicals could be lingering longer than water suppliers expect,” McCurry reiterates. He still recommends staying vigilant. Activated carbon filters can help remove some organic contaminants, but may not completely eliminate the risks.
“Safe water it can rebuild after the fire,” says Whelton. “Communities that recover faster and stronger are those that work together and support each other.”