Dirt-Like Smell in California Water Caused by Algae

July 6, 2016
Santa Clara Valley Water District works to eliminate odor

The Santa Clara Valley Water District in California is working to minimize or eliminate a dirt-like odor at its water treatment plants.

The smell is purely aesthetic and does not pose a health concern. It 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 water safety is not impacted. However, the human nose is sensitive to geosmin: Some people can smell it at extremely low levels—as low as 1.3 ppt. Levels up to 25 ppt were measured in delta water last week.

At present, the Santa Clara Valley Water District does not know how long or how intense the geosmin episode will be, but is working to rid the treated water of the unpleasant smell.

Water moves from the delta through the South Bay Aqueduct to two of the water treatment plants, Penitencia and Rinconada. Penitencia serves parts of Milpitas and the northeastern part of San Jose, and is equipped with ozone, which can remove approximately 90% of the geosmin. If the compound level does not get too high, the plant could reduce the smell 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% of the geosmin, but the smell will likely still be detectable depending on how high the geosmin levels get.

To avoid that, the water district is requesting a change of source from South Bay Aqueduct water to San Luis Reservoir water. It is planned to take place for two days, with potential to extend if necessary. While San Luis Reservoir does have geosmin, it is not at the high level the delta water is experiencing now.

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

Customers who 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. The ongoing monitoring for algal toxins, in addition to monitoring for geosmin, indicates there are no toxins in the water. The water district will strive to improve the taste and smell of the water in this unusual time.

To learn more about taste and odor issues, visit http://valleywater.org/Services/TasteAndOdorFacts.aspx.

Source: Santa Clara Valley Water Distrcit

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