SLO County identifies bacteria contaminating water in Five Cities area
The water contaminant that prompted a boil water alert across the Five Cities area of San Luis Obispo County has been identified.
According to San Luis Obispo County Public Works public information specialist Shelly Cone, the bacteria detected in the Zone 3 distribution system is a coliform bacteria.
In an email, Cone said the detection of coliform bacteria in the environment is an early indication of a potential E. coli contamination.
Cone said the detection of coliform bacteria in the Lopez distribution system was “unprecedented” in the water supply and could affect as many as 50,000 people.
This is the first time an incident of coliform bacteria contamination at the Lopez distribution system has triggered a boil water notice, according to an update Thursday afternoon from the Department of Public Works.
“The presence of coliform does not necessarily mean the water is unsafe, but it does trigger further testing to rule out the presence of harmful pathogens,” Cone said in an email. “If coliform or E. coli is detected, follow-up sampling is immediately conducted until no evidence of contamination remains.”
Multiple cities are clear of coliform contamination, but advise caution
Though the level of coliform contamination is above acceptable levels at the Lopez distribution facility, not all cities have detected the contaminant to the same extent.
In its Thursday update, the Department of Public Works said all affected cities and community service districts are conducting their own water testing, meaning the boil water notice may be lifted on a community-by-community basis.
In a video posted to its Facebook page video, Pismo Beach city manager Jorge Garcia said that while tests on the city’s water all came back negative for contamination, it will continue abiding by the county and state mandates to boil water.
Arroyo Grande city manager Matt Downing similarly said that contamination levels were within acceptable levels there, but he still advised residents to boil water as a precaution.
In a Reel posted to Instagram, Arroyo Grande Mayor Caren Ray Russom said the city was operating under an abundance of caution on the contamination.
“Please take every precaution,” Russom said. “Please use bottled water or boiled water.”
In an email, Grover Beach city manager Matt Bronson said the city’s water testing has produced negative results so far, but has temporarily disconnected its water system from the Lopez distribution system, relying on groundwater for the time being.
Grover Beach will continue sharing information today through posts to its website, social media platforms and its existing email distribution list, Bronson said.
According to the Mayo Clinic, symptoms of infection typically begin presenting three to four days after exposure, though you may become ill as soon as one day after exposure or as late as more than a week after.
E. coli bacteria can be harmless or cause mild symptoms such as brief diarrhea, though some strains can cause severe stomach cramps, bloody diarrhea and vomiting, according to the Mayo Clinic.
San Luis Obispo County Health Agency public information officer Thomas Cuddy said residents should seek medical care right away if they experience any of these more severe symptoms:
- Diarrhea or vomiting more than two days
- Bloody stool or bloody urine
- Fever higher than 102°
- Signs of dehydration such as little or no peeing, having very dark pee, being very thirsty, having a dry mouth or throat, feeling dizzy or lightheaded, and crying without tears
- Unexplained bruising or rash with tiny red spots
- Feeling extremely tired or not alert
If you have mild symptoms and are recovering at home, it is important to stay well-hydrated while children exhibiting diarrhea or vomiting symptoms should try to drink extra fluids including Pedialyte, Cuddy said.
How can you keep drinking water clean?
The city advised residents to boil all water for one minute at a rolling boil, allowing it to cool before drinking.
Boiled or bottled water should be used for brushing teeth, drinking and food preparation, according to the release.
Households that are unable to boil water should use one-eighth of a teaspoon unscented liquid bleach per gallon of water to disinfect water, followed by a thorough mixing and allowing it to stand for 30 minutes before using, according to the release.
Cloudy water can be made clearer by running it through a clean cloth and using one-quarter teaspoon of bleach per gallon of water, according to the release.
It should be noted that any approach using bleach can cause water to taste or smell like chlorine, which means the disinfection has worked, according to the release.
Water purification tablets can also work to purify tap water, though manufacturer’s instructions may vary.
Garcia further warned that taps with water filters or reverse osmosis filtration systems are not safe against the bacteria and still require water to be boiled.
Ice made from tap water in freezers and small filtering systems should be disposed of, Garcia said.
Dishes can still be washed under tap water so long as the water is hot — at least 150 degrees — so bottled water may still be preferable for washing dishes and brushing teeth.
Pets are similarly susceptible to the bacterial contamination, and should also only drink bottled water until the issue has been resolved, Garcia said.
Bathing and showering is still safe under the contaminated water, so long as you limit the amount of water that gets in your mouth, though babies and toddlers should be washed with sponge baths out of an abundance of caution, Garcia said.
This story was originally published May 1, 2025 at 11:50 AM.
