Pleasanton and Livermore residents who might have noticed an odd smell coming from their tap water recently have nothing to worry about, according to the Zone 7 Water Agency.
The agency said in a press release that the water is safe to consume and explained that the smell comes from a naturally occurring organic compound called geosmin, which is found in surface water supplies from the Sacramento-San Joaquin Delta during “warm weather algae blooms.”
These algae blooms — which as the name suggests, happen when water is exposed to warmer temperatures — typically occur during the summer.
“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,” she added.
Humans are “biologically hardwired” to detect geosmin even at extremely low levels, according to Zone 7 officials. The agency said the human nose and taste are able to detect the harmless compound at around 15 parts per trillion which, for comparison, if a person dissolved a packet of sugar into an Olympic-sized swimming pool, that concentration would represent 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,” according to Zone 7.
The agency also pointed out that geosmin is the same natural compound responsible for that earthy aroma in the air right after a summer rainstorm.
“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,” officials said.
Zone 7 acknowledged that while not dangerous, the smell is also not ideal.
The agency is mitigating the taste and odor impacts of the seasonal algae growth by continually monitoring its water supply and adjusting its water treatment process, according to the press release.
“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,” O’Brien said.
The agency said its raw water ozonation at its two surface water treatment plants is one of the best ways to “break down taste and odor compounds.”
Zone 7 also reiterated that, despite the temporary earthy smells, its water “continuously meets or performs better than all strict state and federal safety standards.”
As for how residents can address the issue, officials suggest chilling the water or adding some citrus to mask the geosmin.
“Zone 7 Water Agency sincerely thanks the Tri-Valley community for their patience and understanding as (the) water quality team adjusts to these seasonal environmental shifts,” the agency stated in its press release. “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.”
