Water Resources

Local Water Supply

Palo Alto’s water comes from the San Francisco Public Utilities Commission (SFPUC). This high quality water supply consists almost entirely of Sierra Nevada snowmelt delivered through the Hetch Hetchy water distribution system.

Precipitation levels can vary greatly within any given year. Even though we may experience periods of wet weather, a warm dry spell can affect water supplies later in the year. These climate conditions, along with our limited long-term water supplies, mean it is in our best interest to use water as efficiently as possible, regardless of drought conditions. Read the City of Palo Alto's 2015 Urban Water Management Plan. 

Current Water Blend Change from SFPUC

Beginning December 29, the SFPUC will temporarily change the source of our typical water supply from the Hetch Hetchy Reservoir. SFPUC will deliver water from local surface reservoirs along the Peninsula. This is necessary to accommodate inspections and repairs of the Mountain Tunnel pipeline that delivers water from the Hetch Hetchy Reservoir.

The Hetch Hetchy shutdown is anticipated to continue through the beginning of March 2017. During this period, SFPUC will provide its wholesale customers (cities including Palo Alto, counties and water districts on the Peninsula) with treated water from the Sunol Valley and Harry Tracy Water Treatment Plants. In preparation for the Hetch Hetchy shutdown, SFPUC began taking water from the Sunol Valley Treatment Plant on December 23. Starting on December 29, these facilities will each provide about 80 million gallons per day (mgd) as supply to the SFPUC Regional Water System.

The chart below provides details on the water quality parameters anticipated as a result of this blend change.

Potential Change in Taste, Color or Odor

A change in water blend can alter the water aesthetics (taste, color or odor), as it is being mixed with water from another source location. It can stir up sediment or algae in the water distribution system. Some people may notice a more earthy or musty taste or odor in the water. This typically subsides after a few days. Customers can try running the cold water (not hot) for a few minutes to clear out water in pipes or consider using a filter to alleviate taste or odor issues.

SFPUC has told its wholesale customers that the agency will do all it can to mitigate taste and odor issues with this current blend change. Curious about the blend event from early December that caused some concern about a more significant change in taste and odor? Read an update from SFPUC here:  http://sfwater.org/index.aspx?page=884

The City of Palo Alto Utilities (CPAU) and SFPUC test your water daily to ensure it meets drinking water quality standards and will continue to monitor conditions very closely. We will provide updates as necessary. Please contact our Water Transmission staff at (650) 496-6967 with any questions about water quality or blend changes.

The following table compares water quality parameters at Irvington Portal. This data is based on the most recent sampling results and represents an estimate of how the blend parameters will change.


As of 1-24-17

As of 1-25-17

HH Flow (MGD)









Total Chlorine Residual (mg/L)



Free Ammonia-N (mg/L)






Turbidity (NTU)



Conductivity (uS/cm)



Hardness (mg/L)



Alkalinity (mg/L)



TOC (mg/L)



Palo Alto Water Quality

The City of Palo Alto Utilities and our water supplier are required by law to adhere to strict health and safety standards for potable drinking water. Every year we publish an annual water quality report, which informs customers about the City's water quality. General questions or concerns? Call us at (650) 329-2161 to report issues or request information.

Annual Water Quality Report

Your water has a variety of physical, chemical and biological elements that are described in more detail in our annual water quality report. This report is updated every year and made available to our utility customers. Past annual reports are provided below on this webpage.

Highly Sensitive Customers

Since occasional minor fluctuations in water quality can occur, we encourage people who may be vulnerable to drinking water contaminants to seek advice from their health care provider, who may recommend taking precautionary measures such as adding filtration devices.
Please contact our Water Transmission division at (650) 496-6967 with any questions about water quality or blend changes.

Water Distribution System Flushing

City staff need to periodically flush water mains and hydrants with fresh water to prevent the water quality from degrading. This is more frequently needed in areas where a cul-de-sac or end-of-the-line piping tend to accumulate vegetation, algae or sediment. Flushing is necessary to keep debris out of customers' service line. We post signs at each site to let people know that this is being done.

We monitor our water quality every day to ensure that it meets all State and Federal guidelines for drinking water quality standards. If a customer experiences discoloration or sediment in water coming from the tap, they should flush the cold (not hot) water for a minute or more until the water clears.


Get the facts
 about fluoride in drinking water. Read more from the Centers for Disease Control, American Dental Association, Environmental Protection Agency, and DrinkTap.org. You also read more at theSFPUC fluoridation page.

Chromium 6

Chromium is an abundant element in the Earth’s crust, found naturally in rocks, plants, soil and volcanic dust, humans and animals. One form, hexavalent chromium, is widely found in waters, including source waters for drinking water, typically at VERY low concentration levels.
Chromium 6 is not a concern in Palo Alto.

The water supplies we receive from the SFPUC fully comply with the new California Chromium 6 MCL standard finalized in July 2014. Click here for the latest SFPUC report on Chromium 6. Read more from the American Water Works Association on this topic. For detailed information about your water in Palo Alto, visit our water quality report. 


The City of Palo Alto takes its responsibility to protect customers from lead exposure very seriously. Palo Alto Utilities does not have lead services or other equipment in our system, though we still perform sampling to ensure clean, safe drinking water quality. Currently, we are working with Palo Alto Schools on plans to test lead levels in any requested K-12 school site. The City of Palo Alto’s lead sampling technique uses best practices for accurate water quality testing. If you have questions about the CPAU lead or other water quality testing procedures, please contact our Water Transmission Staff at (650) 496-6967.

Read more on Palo Alto's Water

SFPUC Hetch Hetchy System Operations

  • Watch a presentation about the SFPUC Water System Improvement Project.
  • View a reference map of the SFPUC Hetch Hetchy System.

Previous Palo Alto Annual Water Quality Reports

  • 2014 Annual Water Quality Report. Also available in Spanish and Mandarin.
  • 2013 Annual Water Quality Report. Also available in Spanish and Mandarin.
  • 2012 Annual Water Quality Report.
  • 2011 Annual Water Quality Report.
  • 2010 Annual Water Quality Report.
  • 2009 Annual Water Quality Report.
  • 2008 Annual Water Quality Report

Last Updated: Feb 2, 2017