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Some San Diego area residents told to boil tap water due to possible E. coli contamination

E. coli bacteria was detected in drinking water in Imperial Beach, California.
An electron micrograph scan of Escherichia Coli.
E. coli bacteria has been detected in the water system that serves some San Diego area residents.BSIP / Universal Images Group via Getty Images

Some residents in the San Diego area have been told to boil their tap water and use bottled water for drinking and cooking after E. coli was detected in the drinking water at a site in Imperial Beach, California.

California American Water, the public utility company that services the affected areas, issued the advisory Thursday for residents of Imperial Beach, as well as some parts of nearby Coronado, San Diego and Chula Vista. Those residents should also discontinue nonessential water use such as outdoor irrigation, the company said.

More than 17,000 individual service lines are affected by the advisory, according to Brian Barreto, California American Water's external affairs manager for Southern California.

The company said in a release that it expects to resolve the problem within 48 to 72 hours. 

"We have no reason to believe that the water supply in our system is contaminated or there's been any breach of the integrity of our systems," Barreto said.

Barreto said the first positive sample came back Wednesday, and the company performed additional sampling on Thursday, with plans to sample again later on Friday. The company needs to see two negative results to lift the water advisory, he said.

E. coli is a bacterium that can contaminate food or water. Infections can cause vomiting, severe stomach cramps and diarrhea that is often bloody, according to the Centers for Disease Control and Prevention.

California’s Division of Drinking Water, which regulates public drinking water systems, recommends letting tap water boil for three minutes to kill E. coli bacteria.

The City of Imperial Beach said Thursday night that residents can pick up a case of bottled water at California American Water's operation center in Imperial Beach.

"Our ocean water is poisoned, our air is poisoned, and now our drinking water is tainted. It is beyond time to declare the egregious environmental and public health disaster harming communities of color in San Diego a State of Sewage Emergency," Paloma Aguirre, the mayor of Imperial Beach, wrote Friday in a post on X, formerly known as Twitter.

According to NBC 7 San Diego, several schools in the San Ysidro School District closed on Friday out of an abundance of caution due to the water contamination. The Chula Vista Elementary School District has shut off water, except for toilets, at five schools and is providing water bottles, hand sanitizer and hand washing stations, NBC 7 reported.

Most people who get E. coli infections recover within a week and some people exposed don't get sick at all, depending on the strain. But certain cases can be severe, even life-threatening. People who are young, elderly, pregnant or immunocompromised are more likely to suffer severe outcomes.

It’s not yet clear what the source of contamination was in this case. Barreto said that because the E. coli was detected in an outdoor faucet, it’s possible the bacteria came from an animal sitting on the faucet or licking it.

Georgia Kayser, an assistant professor of global and environmental health at the University of California, San Diego, said E. coli in drinking water is often a sign of fecal contamination.

After a storm, runoff or flooding can carry feces from land into surface water that feeds drinking water systems. Over the weekend, the San Diego area was inundated with heavy rain and winds from Hurricane Hilary, which weakened to a tropical storm before reaching Southern California.

“When you have a big rain event, you have a lot more water to treat. Sometimes that can overwhelm systems," Kayser said. "Sometimes, too, that rain event pulls a lot of E. coli off all the surrounding area into, say, a surface water source or reservoir or some sort of lake or creek that’s being used for for drinking water.”

Generally, though, water systems treat water sufficiently so that E. coli never winds up in people's drinking water, she added.

"It’s more rare to see these advisories, but they do happen," she said.