If you have noticed a sudden, earthy or musty taste and smell in your tap water recently, your nose is working exactly as nature intended. Zone 7 Water Agency wants to reassure Tri-Valley residents that this seasonal aesthetic change poses absolutely no health risk, and the water remains entirely safe to drink and use.
The odor is caused by a naturally occurring organic compound called geosmin, which peaks in surface water supplies from the Sacramento-San Joaquin Delta during warm weather algae blooms. While harmless, humans are biologically hardwired to detect this compound at extremely low levels at around 15 parts per trillion.
To put this scale into perspective:
- The Pool Analogy: If you dissolved an ordinary, single packet of sugar into a massive Olympic-sized swimming pool, that concentration represents 1 part per billion. Finding 1 part per trillion is the equivalent of trying to taste a fraction of less than one single grain of sugar inside that entire pool.
Geosmin is the exact same natural compound responsible for the pleasant, earthy aroma you notice in the air right after a summer rainstorm (a phenomenon known as petrichor). Because our senses are so sharp, we can easily pick up this familiar outdoor scent even when it is present in almost imperceptible amounts that have absolutely no impact on the safety of your drinking water.
Proactive Monitoring & State-of-the-Art Treatment
To mitigate the taste and odor impacts of seasonal algae growth, Zone 7 is continuously monitoring water supplies and dynamically adjusting treatment processes.
The primary line of defense is raw water ozonation at the agency's two surface water treatment plants. Ozonation is a best-in-class technology specifically suited to break down taste and odor compounds.
"Our lab team is running tests and gathering data around the clock to track these seasonal shifts," said Angela O'Brien, Zone 7 Water Quality Manager. "While geosmin creates a highly noticeable scent, it is strictly an aesthetic issue. We are continually adjusting our state-of-the-art treatment processes, including our ozone systems, to neutralize the odor and ensure every drop delivered meets our stringent quality and safety standards."
Residents can watch a short educational video detailing how our state-of-the-art ozonation system works at https://youtu.be/fWvuZdQCjtQ?si=eS0-DH4aw6GO3nV
Exceeding Stringent Quality Standards
Despite the temporary earthy smell, Zone 7 water continuously meets or performs better than all strict state and federal safety standards. The agency operates under highly rigorous internal water quality targets designed to maintain an additional margin of safety for the community.
Residents looking for a deeper dive into local water safety can review the newly released Zone 7 Annual Water Quality Report. This comprehensive report outlines the agency's extensive testing protocols, advanced infrastructure investments, and track record of delivering clean, reliable drinking water straight to your kitchen tap.
Tips for Homeowners
While treatment adjustments to mitigate this temporary odor are underway, residents can significantly reduce the earthy taste at home by:
- Chilling the water: Keeping a pitcher of tap water in the refrigerator minimizes the perception of the odor.
- Adding citrus: Squeezing a wedge of lemon or lime into the water effectively masks the geosmin flavor.
Zone 7 Water Agency sincerely thanks the Tri-Valley community for their patience and understanding as water quality team adjusts to these seasonal environmental shifts. Delivering clean, reliable, and high-quality drinking water that meets all safety standards remains the agency's top priority, and Zone 7 continues to work diligently to resolve these temporary aesthetic impacts as quickly as possible.
Photo courtesy of Zone 7 Water: Advanced ozonation infrastructure at the Patterson Pass Water Treatment Plant. This system is actively used to target and remove seasonal taste and odor compounds from our surface water supply.
About Zone 7 Water
Zone 7 Water Agency is one of the 10 active zones of the Alameda County Flood Control and Water Conservation District. The District was established by the State Legislature in October 1949 to solve problems of flooding, drainage, channel erosion and water supply and conservation in Alameda County. In 1957, by popular vote, Zone 7 became a special district governed by a seven-member board of directors. Along with flood protection, Zone 7 supplies water to all of eastern Alameda County and a population of over a quarter million residents. Treated water is sold wholesale to local retailers, including the cities of Livermore and Pleasanton, the Dublin San Ramon Services District, and the California Water Service Company. Zone 7 also distributes untreated water to local agriculture operations and golf courses.
Zone 7 Water
-
Alexandria Bradley Community Service
- June 30, 2026
- (925) 454-5000
- Send Email
