If you live in the Tri-Valley and something seems a bit funky with your tap water recently, it’s not all in your head (or nose.)
Some Tri-Valley residents have been noticing an earthy or musty taste and smell in their drinking water, but Zone 7 Water Agency says the water remains safe to drink and use. The City of Pleasanton also issued a notice saying the temporary condition is affecting multiple Tri-Valley water agencies.
What Is Causing The Smell?
The likely culprit is geosmin, a naturally occurring organic compound that can show up in surface water supplies during warm-weather algae blooms. Zone 7 says the compound is common in the Sacramento-San Joaquin Delta during seasonal algae activity and can create a noticeable earthy or musty scent, even at extremely low levels.
Zone 7 even notes that geosmin is the same natural compound behind the familiar earthy smell in the air after a summer rainstorm. The agency says the issue is “strictly an aesthetic issue,” not a health risk.
Why It Is Happening Now
The timing appears to be tied to both seasonal algae and recent water system operations.
Pleasanton officials said the temporary taste and odor change was associated with seasonal algae in the source water, along with planned State Water Project maintenance conducted by Zone 7 from June 27 through July 2. During that period, source changes and treatment operations may have made the taste and odor more noticeable.
Zone 7 had also asked residents and businesses to temporarily reduce outdoor water use during the maintenance period because a key portion of the State Water Project serving the Tri-Valley was temporarily unavailable while the California Department of Water Resources completed upstream work.
That conservation request has since ended for Livermore-area Cal Water customers, with Cal Water saying the maintenance work was completed as of July 2.
Who Gets Water From Zone 7?
Zone 7 is the Tri-Valley region’s water wholesaler. Its 2025 consumer confidence report says the agency provides water to four major water retailers and a small number of direct customers, serving more than a quarter-million people in Pleasanton, Livermore, Dublin, and the Dougherty Valley area of San Ramon.
The agency’s water comes from a mix of imported surface water, local surface water, and groundwater. A large share of the region’s supply originates as Sierra Nevada snowmelt, moves through the State Water Project and Delta, and reaches the Tri-Valley through the South Bay Aqueduct.
Surface water systems can be more prone to seasonal taste and odor swings, especially during hot weather.
Officials Say The Water Still Meets Standards
Zone 7 says its water continues to meet or perform better than state and federal safety standards despite the temporary smell. Pleasanton said Zone 7 performs water quality testing throughout the treatment process, while the city is also collecting samples in its distribution system to confirm water quality.
DSRSD, which serves Dublin and the Dougherty Valley area, gives a similar explanation on its water quality page, saying seasonal algal blooms in the Delta can cause Tri-Valley tap water to smell or taste earthy or musty, while Zone 7’s treatment processes keep the water safe and in compliance with state and federal standards.
What You Can Do At Home
For residents bothered by the taste, there’s apparently an easy fix.
Zone 7 and Pleasanton both recommend keeping an open pitcher of tap water in the refrigerator to help the odor dissipate. Zone 7 also suggests adding lemon or lime to mask the geosmin flavor.
DSRSD adds that a basic carbon-based filter, such as a pitcher filter or faucet attachment, can also help improve taste.
We’ll continue to follow this story, especially if the taste worsens. Make sure to join our free 925 News newsletter so we can keep you updated.
