Unpleasant odors and flavors reported in drinking water this week are caused by a harmless algae byproduct, San Francisco water officials said Thursday.
San Francisco Public Utilities Commission officials have found evidence of the substance, known as geosmin, at the Sunol Valley Water Treatment Plant and have taken steps to take the plant and the San Antonio Reservoir that feeds into it offline while they work to flush the system.
However, it could be as much as a week in some areas before the water returns to normal.
SFPUC Assistant General Manager Steve Ritchie said the water department began receiving customer complaints of earthy, musty flavors and odors on Friday, shortly after employees began taking steps to lower the water levels in local reservoirs in anticipation of rain.
Officials initially assumed the issue was related to sediment in pipelines, and standard tests did not show any problems. However, after the complaints continued, the agency conducted more detailed analysis that detected the algae byproduct.
Ritchie said the problem was missed initially because it is extremely unusual to have algae problems in the cooler winter months, and no algae bloom is evident at the San Antonio Reservoir, the presumed source of the algae.
Despite the fears of some residents, however, Ritchie emphasized that the water is completely safe.
“The water meets all water quality standards and is truly safe to drink,” Ritchie said.
The San Francisco Health Department issued a supporting statement today noting that the SFPUC’s water treatment removes all algae but cannot remove the byproducts, which can produce the odors and flavors even at very low concentrations.
“These compounds are harmless to humans and pose no health risk when water containing them is consumed or when exposed to their odor,” the health department said.
The SFPUC supplies water to 2.6 million customers in the Bay Area from both the Hetch Hetchy Reservoir in Tuolumne County and from local reservoirs. Customers are typically supplied with water from a mix of sources that changes throughout the year in response to system conditions.