Backflow

Note: If you have recently been notified that you are required to install a backflow prevention device, visit our Backflow Installation Instructions page for instructions and other information to help you through the process!  Special information for private well owners is also included.

Backflow Prevention Devices and Who Needs One

Backflow devices are an integral part of the City’s Cross Connection Control Program. They help to ensure that no contaminants of any kind (chemicals, debris, reclaimed water, etc.) enter the potable water system. 

Backflow devices are owned by the customer and regulated by the State through the City of Palo Alto.  While it is primarily business customers who are required to have these devices, some residential properties need them, also. The State of California Department of Health Services provides regulations for the City and our customers through California Code of Regulations, Title 17. These regulations spell out the types of services that require backflow devices. 

Check out our general guide(PDF, 29KB) to understanding and installing backflow prevention devices.

Questions about the backflow prevention device survey, testing, or test reporting? Please contact the City's Cross-Connection Control Office at (650) 496-5926.

Trying to install a backflow prevention device?

If you have already looked for the correct location for your device but still need further assistance, our Building Department can assist you. Please contact the Building Department at (650) 329-2496.

Please do not ask plumbers bidding on your job to contact the inspectors. Only you or a plumber who is already contracted for the work should be in contact with the inspectors. This eliminates confusion and allows our staff to give you more efficient service.

Backflow Standards

• WD-11A 3 in or Larger Reduced Pressure Principle Assembly - RPPA(PDF, 127KB)
• WD-11B Parallel Reduced Pressure Principle Assembly - RPPA(PDF, 136KB)
• WD-11C Reduced Pressure Principle Assembly RPPA (0.75-2 in(PDF, 152KB))
• WD-12A Reduced Pressure Detector Assembly - RPDA for Fire Services and Sprinklers(PDF, 139KB)
• WD-12B Reduced Pressure Detector Assembly - RPDA for Inside Installation(PDF, 115KB)
• WD-12C Residential Double Check Valve Assembly - DCVA (1-2 in)(PDF, 171KB)

Backflow Prevention Survey

The State requires all water utilities to complete an inventory survey of all properties to ensure every location which requires "backflow prevention devices" has one. The City of Palo Alto is currently modifying its plans on how to survey the City. Please stay tuned for more information. Thank you for doing your part and protecting the City’s water system! 

If you are a Utilities customer who has been directed to install a backflow prevention device on your water main, we want to make the process as easy as possible for you!

You can obtain general instructions about the process and contact information for assistance by viewing the Backflow Prevention Device Installation Guide(PDF, 29KB).

For important advice about backflow issues if you also want to "go green" and use rain barrels, recycled "gray water" or install solar water heating, please view our "When You Go Green" tab.

For further installation information please visit the Building Department's website or see a few helpful links below:

• The Building Department's Online Permit System lets you deal with the process from your home or office. 
• Public Works Department Information and Forms 

Private well owners - Wells are the jurisdiction of the Santa Clara Valley Water District (SCVWD). Well installations and removals must be coordinated through them. Visit the SCVWD website to learn more. 

As a courtesy to our customers who are interested in having an existing well removed, we provide links to the SCVWD’s Well Guidelines and Demolition Applications below. Please note that well documents are the property of the Santa Clara Valley Water District and may change without notice. To be sure you are reading the most up-to-date information, you should contact the SCVWD directly.

• SCVWD Guide for Private Well Owners.
• SCVWD Well Permits and Inspections.

The City of Palo Alto does require backflow prevention on all water services to any properties with wells. This will include any properties served or crossed by well service; even if the well is not at that property.

If you have any questions or concerns about whether you fall under the mandatory requirement to install backflow prevention devices, please feel free to call our staff at (650) 496-5926 or email us

Backflow Device Testing Procedures

Once backflow devices are installed, the devices must be tested on an annual basis and test results must be submitted to the City. Your City approved tester will place a serialized, color-coded, metal tag on your device that will be changed out each year.

The City will only accept test reports from testers who have registered with the City of Palo Alto and have provided the Cross Connection Control Program with copies of their State certification and calibration reports. Please see our list of registered testers(PDF, 97KB). 

Testers wishing to register with the City may contact the Cross Connection Control Program office at (650) 496-5926 or via email.

All tests results must be submitted on a City of Palo Alto test form(PDF, 119KB).

Questions about the backflow prevention device survey, testing, or test reporting? Please contact the City's Cross-Connection Control Office at (650) 496-5926.

Be Water Safe and Water Smart

Customers who want to "go green" in their water usage, need to realize that while a great idea, some of these "green" options do require the installation of backflow prevention devices to protect the public drinking water system.

Using Barrels to Collect Rainstorm Water

Find out more about the City’s rain barrel program.

The City of Palo Alto does NOT require a backflow device for rain barrels as long as they remain stand-alone devices and are not connected to your home’s plumbing or irrigation system.  If you would like to incorporate your rain barrel(s) into a plumbed system, a backflow device will be required on every incoming water service to the property.

Installing a Solar Water Heater

At this time, the City of Palo Alto does not require backflow devices for residential properties that do not contain any chemical additives and are considered "Once Through” systems---meaning a system where the water simply passes through the solar unit before going through the standard hot water heater.

Commercial properties and residential systems that contain chemical additive agents are required to install backflow devices on all incoming water services.

Installing a Gray Water (Recycled) System

At this time, the City of Palo Alto requires backflow prevention devices on all water services to any properties with gray water systems, except the systems commonly referred to as “Laundry to Landscape”.  For recycled systems other than Laundry-to-Landscape, the high coliform content in gray water, simple Pressure Vacuum Breaker (PVB) or hose bib style protectors are not adequate protection – a Reduced Pressure (RP) assembly is required.  However, Laundry-to-Landscape systems are not a problem in this regard and in fact, are a good way to reduce water use, especially during the current drought.  In partnership with Palo Alto Utilities, the Santa Clara Valley Water District is offering $200 rebates for such systems--visit the SCVWD website for more details.

For further information about backflow prevention devices in general or as they apply to the "green" measures above, contact the Cross Control Connection Office of the Utilities Department at (650) 496-5926.