Residents near Half Moon Bay are being ordered to boil their tap water after a main break possibly contaminated the local supply, officials said Tuesday.
About 150 residents in the unincorporated El Granada neighborhood in San Mateo County have been under the order since Sunday afternoon, when a 10-inch water main ruptured and rapidly reduced pressure in the Coastside County Water District System, said General Manager David Dickson.
The main leaked for about an hour and spilled at least 100,000 gallons, Dickson said. The district issued the boil water order out of "an abundance of caution" because the low pressure could cause some homes' water to flow backward into the system, contaminating it, Dickson said.
A water sample taken Monday morning was negative for bacteria, Dickson said. Officials took a second sample Tuesday morning that takes 24 hours to develop. If the results are negative again, the boil mandate will be lifted.
"It's an extremely rare event and one we pay attention to," Dickson said.
The water district has about 7,000 customers and serves a population of about 17,000 people in and around Half Moon Bay.