Water users in San Diego County may notice a musty taste and odor in their tap water caused by algae blooms in Diamond Valley Lake near Hemet in Riverside County, the Metropolitan Water District of Southern California said Tuesday.

MWD oficials said the taste and odor may go away by the end of the week because affected facilities and supplies were treated over the weekend. They stressed that the water is safe to drink.

“The earthy taste and smell stem from an algae bloom in Diamond Valley Lake near Hemet in southwest Riverside County, which is affecting supplies being delivered to the San Diego County Water Authority,” said Jim Green, MWD’s manager of water system operations.

“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,” he said, adding that refrigerating the tap water will improve the taste.

The algae bloom began at Diamond Valley Lake, and affected supplies in nearby Lake Skinner north of Temecula.

Growth of algae in open surface reservoirs is generally a seasonal problem that usually occurs in warm months, according to the MWD. As in previous years, the cause of this year’s taste-and-odor episode has been identified as geosmin, a nuisance compound produced from the growth of certain algae in freshwaters throughout the world.

“Unfortunately, people with sensitive taste and smell can detect the compound in water at levels as low as 5 parts-per-trillion,” Green said. “By comparison, one part-per-trillion is equivalent to just 10 drops of geosmin in enough water to fill the Rose Bowl.”

The San Diego water authority receives most of its supply from the MWD, but has been developing independent sources in recent years.

Chris Jennewein

Chris Jennewein is Editor & Publisher of Times of San Diego.