Earthy smell in water caused by algae

If you have noticed an earthy smell in your tap water, we want you to know that we are aware of it and are working to correct the odor that, while unpleasant, does not pose a health concern.

The smell is affecting parts of Santa Clara, Sunnyvale, Campbell, Saratoga, Monte Sereno, Cupertino, Mountain View, Los Altos and Los Gatos, and to a lesser extent south San Jose, and is purely aesthetic. Our water still meets or surpasses drinking water standards.

The earthy odor is caused by geosmin, a compound produced by algae that has recently bloomed in the Sacramento-San Joaquin Delta and the San Luis Reservoir, 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 48 ppt have been measured in the source water and treated water.

At present, we expect the intense geosmin odor to subside in a few days as the water already in the distribution system works its way out. We have changed the source of water at our Rinconada and Santa Teresa water treatment plants to a local reservoir that has not been affected by the same odor. We are also increasing treatment at our three water treatment plants to rid our treated water of the unpleasant smell.

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.

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.


  1. I live in West San Jose in the Winchester Orchard neighborhood off of Stevens Creek & Cypress and have the same issue! It’s been like this for awhile now.


  2. Thanks for letting us know, Dottie. Hopefully, you’ll see a difference soon due to the changes we’ve made. We’re working to get this resolved.


  3. I developed an ear infection that needed a huge amount of treatment (2 treatments of antibiotics from my primary care physician, then a “vacuuming” and powdered antibiotic from an ENT specialist), shortly after getting this bad-smelling water in my ear. The ear has finally officially healed as of this week. Purdue University seems to have recently been doing work on treating algae blooms, and in the article they mention that these blooms are toxic to humans. I am really not sure why the Water Co says that it is safe to use this water; I think that the Water Co should publish a little bit more information on WHY the water is safe, so that we know to believe the PR story.


    1. Kim,
      Thank you for your comment. We are happy to provide some more information on why the drinking water we provide is safe. There are different types of algae that bloom from time to time in the Delta and reservoirs. Sometimes, the algae that blooms can be toxic, causing harm to humans and animals that swim or wade in the water. Note that swimming and wading are not allowed in any of our reservoirs. Other times, a different type of algae blooms that is not toxic but creates a byproduct that gives it a certain taste or odor. That is what is happening now. The algae that is blooming is not the kind that creates toxins, and is acknowledged by the EPA as such, but it does leave an unpleasant odor, which is what we are dealing with now.

      Regardless of the type of algae that’s blooming, we monitor for taste and odor issues and for algal toxins. Before the water passes from us to our local water providers, it will undergo percolation into our groundwater, which acts as a natural filtration, or it will go through one of our water treatment plants, where it receives treatment that is effective at removing toxins. This treatment and natural filtration clean the water so that it meets or exceeds all state and federal drinking water standards. Providing safe, clean water for drinking, cooking, bathing and all other uses is extremely important to the water district, and that’s why we test our water frequently at our state-of-the-art water quality lab.

      To learn more about taste and odor issues, please visit our website at


      1. Dear Colleen Valles,

        Thank you so much for your detailed reply to my concerns! I appreciate knowing a little bit more about different types of algaes, and that the water district tests for algal toxins frequently at your state-of-the-art water quality lab. I feel confident the water district is doing an excellent job keeping our water clean for drinking and bathing, and keeping the public informed.

        Kind regards,


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