Water runs from a faucet into a drinking glass.
Central Coast, California – A major public health advisory is in effect across California’s Central Coast after potentially harmful bacteria was discovered in the drinking water supply serving approximately 46,000 residents. Authorities have issued a mandatory boil water notice impacting the “Five Cities” region—Arroyo Grande, Grover Beach, Oceano, Pismo Beach, and Avila Beach—following the detection of coliform bacteria in multiple water samples earlier this week.
Water samples collected on April 28 and 29 tested positive for coliform bacteria, which, while not necessarily dangerous on its own, can signal the presence of more serious contaminants like E. coli. The State Water Resources Control Board and San Luis Obispo County officials are now conducting additional tests and investigations to determine the source and full extent of the contamination.
“This is the first time a boil water notice has been triggered for the Lopez distribution system,” county officials said in a statement Thursday. “We are still working to identify the cause. Repeated positive samples of total coliform triggered a mandatory boil order by the State Division of Drinking Water.”
Until the issue is resolved—expected by Sunday, May 4—residents are urged not to drink tap water unless it has been boiled for at least one minute, or to use bottled water. The advisory also warns residents to be cautious while bathing, especially with babies and young children, and to avoid swallowing water. Ice made from tap water should not be used, and pets should also be given boiled or bottled water.
Pismo Beach City Manager Jorge Garcia emphasized that filtered tap water is not a safe alternative. “Having a water filter or a reverse osmosis system is not sufficient,” Garcia said in a Facebook video Thursday evening.
Despite daily tests in some cities like Pismo Beach returning normal results, all five affected cities remain under the advisory as a precaution. Officials confirmed that laundry may still be done with tap water.
The Mayo Clinic notes that symptoms of E. coli infection—which can include diarrhea (sometimes bloody), stomach cramps, nausea, and vomiting—can appear between one to seven days after exposure.
San Luis Obispo County is providing updates and disinfection instructions via city websites, and urges residents to remain vigilant until the all-clear is given.
