Alert 9/29/20 | 2:57 PM: COVID-19: The water supply remains safe; Valley Water monitoring impacts from wildfires LEARN MORE HERE
Keep Updated
Find events and articles on a wide range of topics
Stewardship header
Page Title
News & Events
Back to top

Possible dirt-like smell in water caused by algae

June 28, 2016

Odor is not a health issue, but District works to eliminate it

SAN JOSE—Some water users may notice a dirt-like smell coming from their tap water. The odor is purely aesthetic and does not pose a health concern; our water still meets or exceeds drinking water standards. Nonetheless, the Santa Clara Valley Water District is working to minimize or eliminate the odor at its water treatment plants.

The smell is caused by geosmin, a compound produced by algae that has recently bloomed in the Sacramento-San Joaquin Delta, where the water district gets more than half of the water it supplies to northern Santa Clara County. Geosmin is not an algal toxin, so the safety of the water is not impacted.

However, the human nose is very sensitive to geosmin: some people can smell it at extremely low levels – as low as 1.3 parts per trillion (ppt). Levels up to 25 ppt have been measured in Delta water this week.

At present, we do not know how long or how intense the geosmin episode will be, but we are taking strides to rid our treated water of the unpleasant smell. 

Water moves from the Delta through the South Bay Aqueduct to two of our water treatment plants, Penitencia and Rinconada. Penitencia serves parts of Milpitas and the northeastern part of San Jose, and it is equipped with ozone, which can remove approximately 90 percent of the geosmin. If the compound level does not get too high, that means we could reduce the smell back down to undetectable levels.

Rinconada, which serves the western part of the valley including parts of San Jose, Santa Clara, Sunnyvale, Campbell, Cupertino, Mountain View and Los Gatos, is undergoing a massive reliability improvement project right now. It does not yet have ozone, which is slated for a later part of the project.

However, Rinconada does have powdered activated carbon, which can remove 10 to 30 percent of the geosmin, but the smell will likely still be detectable, depending on how high the geosmin levels get.

To avoid that, we are requesting a change of our source from South Bay Aqueduct water to San Luis Reservoir water. That is currently planned to take place for two days, and we are looking to extend that if necessary. While San Luis Reservoir does have geosmin, it is not at the high level the Delta water is experiencing now.

Our Santa Teresa Water Treatment Plant, which serves south San Jose, remains unaffected.

As we work to mitigate geosmin’s effect on our water, customers who do experience a taste or odor can chill their tap water before drinking in order to make taste and smell issues less noticeable. It is not necessary to boil water as the water is safe to drink and meets all state and federal public health standards. Our ongoing monitoring for algal toxins, in addition to monitoring for geosmin, indicates that there are no toxins in the water we are receiving.

The water district will strive to improve the taste and smell of the water in this unusual time. We put the highest priority on providing safe, clean water to Santa Clara County.

Learn more about taste and odor issues at:  

Valley Water manages an integrated water resources system that includes the supply of clean, safe water, flood protection and stewardship of streams on behalf of Santa Clara County's 2 million residents. The district effectively manages 10 dams and surface water reservoirs, three water treatment plants, an advanced recycled water purification center, a state-of-the-art water quality laboratory, nearly 400 acres of groundwater recharge ponds and more than 275 miles of streams. We provide wholesale water and groundwater management services to local municipalities and private water retailers who deliver drinking water directly to homes and businesses in Santa Clara County.