Starting this week, some SFPUC customers, who include Castlewood users, may see tap water that appears cloudy or milky-white in color but is nevertheless perfectly safe to drink, spokeswoman Maureen Barry said.
Customers in the city of Pleasanton, which has its own water department and service, and those in Happy Valley who access their water supplier from individual wells, are not affected by the SFPUC advisory.
The change in the water is due to tiny air bubbles caused when an increased rate of flow from the agency's Sunol Valley Water Treatment Plant allows air to be mixed into the water.
If the water is allowed to stand for a few minutes, the cloudiness will dissipate as the air bubbles rise to the surface and break apart.
Due to maintenance on the regional water system, SFPUC customers are not receiving water from the Hetch Hetchy Reservoir in the Sierra Nevada, but rather local reservoirs in the East Bay and Peninsula.
The cloudiness is expected to dissipate when Hetch Hetchy supplies reach the Bay Area again after the completion of the work, which is scheduled to finish late next month.
Customers in Alameda and Santa Clara counties are most likely to see the cloudiness, according to Barry. As the water works its way through the system, up the Peninsula and into San Francisco, the air bubbles will not be as apparent, she said.
The SFPUC is emphasizing that the cloudy water is "nothing to cause concern," Barry said. The water continues to meet all state and federal regulatory requirements for water quality.
She said the same thing has happened in recent years, and although the agency did not receive many calls about the cloudy water last year, "it could happen, so we didn't want to alarm anyone if it does over the holidays."