Claremont residents may be experiencing a musty taste and odor in their tap water, but it is an aesthetic problem caused by an algae bloom and not a health hazard, according to water quality experts.

Officials at the Metropolitan Water District of Southern California said the taste-and-odor event is affecting tap water in eastern Los Angeles County communities—including Three Valleys Municipal Water District, which services Claremont—as well as southwestern San Bernardino County. The impacts may vary as local agencies blend imported Metropolitan water with local supplies.

The earthy taste and smell stem from an especially large and persistent algae bloom in the east branch of the State Water Project, according to Jim Green, Metropolitan’s manager of water system operations.

“We are working with the State Department of Water Resources (DWR)—which owns and operates the state system—to address the situation,” Mr. Green said. “Consumers, however, can be assured that the taste-and-odor issues they may be experiencing in their tap water do not pose any health risks.”

The cause has been identified as both 2-methylisoborneal, or MIB, and geosmin. These nuisance compounds are produced from the growth of certain algae in freshwaters throughout the world.

“Unfortunately, people with sensitive taste and smell can detect these compounds in water levels as low as 5 parts-per-trillion,” Mr. Green said.

Mr. Green suggested refrigerating drinking water to help improve its taste until the problem diminishes. Though DWR water quality experts recently applied copper sulfate, an approved method, to control the algae bloom, Mr. Green cautions the problem may persist for another couple weeks. Officials stressed that the treated water will be safe for consumers. Fish and wildlife also will not be impacted.

Consumers interested in receiving additional information about the quality of Metropolitan’s drinking water supplies can visit the district’s website, mwdh2o.com, for the district’s annual water quality report and other related materials.