Water Resources

Flushing Guidance for Buildings Following Shutdown

Businesses are returning to work after an extended shutdown due to COVID-19 public health shelter in place orders. If a building has been vacant and dormant, water use has been reduced, which could result in a degradation in water quality. Stagnant water can harbor bacteria, so it is important to flush your water system before you begin using the water again. Our water supplier has provided guidance with steps to take when restoring water service.  

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. There since has been minor edits to the 2015 Urban Water Management Plan.

Water Quality & Annual Consumer Confidence Report

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 Consumer Confidence Report which informs customers about the City's water quality. This report is also available in Mandarin and Spanish. Past annual reports are provided below on this webpage.  If you would like a copy of the report mailed to you, please email us at UtilitiesCommunications@cityofpaloalto.org or call (650) 329-2417 to submit a request. Click here for the 2016 Public Health Goals Report. Read about tap water quality versus bottled water. 

Water Quality Parameters

As of October 18, 2020:  The Hetch Hetchy Aqueduct (HH) is currently providing about 180 MGD of supply. On Sunday, October 18, the Sunol Valley Water Treatment Plant (SVWTP) will come into service to supplement the Regional Water System supply.  On Monday, October 19, the Harry Tracy Water Treatment Plant (HTWTP) will be placed in standby for maintenance activities.  This operational configuration is expected to last for a month. 

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.  Some fluctuations in water quality parameters may occur while adjustments are made during the source water transition. 


 Parameter As of 10/15/20 As of 10/19/20
HH Flow (MGD)   180 180
HTWTP Flow (MGD)  40 0
SVWTP Flow (MGD)  0 40
 Total Chlorine Residual (mg/L)  3.0 3.0
 Free Ammonia-N (mg/L) 0.04 0.04
 pH 9.5 9.6
 Turbidity (NTU) 0.2 0.18
 Conductivity (uS/cm) 51 113
 Hardness (mg/L) 10 31
 Alkalinity (mg/L) 13 34
 TOC (mg/L) 1.4 2.0

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.


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. The City of Palo Alto’s lead sampling technique uses best practices for accurate water quality testing. If you have questions about the City's lead or other water quality testing procedures, please contact our Water Transmission Staff at (650) 496-6967.


Get the facts about fluoride in drinking water. Read more from the Centers for Disease Control, American Dental Association, and DrinkTap.org. You also read more at the SFPUC 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. Here is the latest SFPUC report on Chromium 6. For detailed information about your water in Palo Alto, visit our water quality report. 

Read more on Palo Alto's Water

Palo Alto’s long-term water supply forecast, water demand and conservation programs in the 2015 Urban Water Management Plan.  (minor edits to the Urban Water Management Plan)

  • Stay Informed! Get updates on breaking news about any water disruptions or quality issues by following us on Twitter @PAUtilities
  • Report a substantial leak, break or other emergency by calling (650) 329-2579
  • Report over-watering or other water waste by emailing drought@cityofpaloalto.org or by calling (650) 496-6968.
  • Read more about water rates & supplies.
  • Backflow prevention surveys--get the full scoop about what is going on and why here.
  • Palo Alto's Recycled Water Plan

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