What is a backflow prevention device?

A backflow prevention device is a precautionary device approved by the State Office of Drinking Water and the University of Southern California (USC) Hydraulic Research Section that provides protection from potentially hazardous substances getting pushed or pulled back into the City water system. In situations where chemicals or contaminated water could possibly backflow due to back pressure or back siphonage, known as a “hazard”, a backflow prevention device is required to protect the integrity of the water distribution system.  

Reduced Pressure Device 

Hazards include a separate irrigation system on a property, a business that uses chemicals, a property with a sewage lift station, or a potential cross connection with an unknown source. All the proceeding hazards are considered “high hazard” situations and require what is known as a reduced pressure backflow prevention device. Reduced pressure (RP) backflow prevention devices have a reduced pressure zone in the center of the device with two independent working check valves that prevent water from flowing back into the water system. This device is required in high hazard situations per State Health Code Title 17.

Double Check Device

Properties might have “low hazards” such as a well, pumps, or a residential fire sprinkler system. Properties with low hazards are required by State Health Code Title 17 to install a double check (DC) backflow prevention device. The double check backflow prevention device is a valve assembly with two independent spring-loaded check valves that allow water to flow through the device to the property but prevent water from flowing backwards.



In-line Dual Check Valve

The In-line Dual Check Valve is a mechanical device designed to prevent backflow and back-siphonage into the drinking water system, it consists of two independently acting, spring-loaded check valves. Designed for use in “low hazard” cross-connections and continuous pressure applications. The intended application is for residential water systems at the service entrance to fire sprinklers. 

Because it is not a testable backflow prevention device, the In-line Dual Check Valve is exempt from the yearly testing requirement. To ensure that the device is functioning properly, In-line Dual Checks must be replaced every 5 years. At this time, the In-line Dual Check is allowed for properties affected by the 2017 Tubbs-Adobe Fires only.

Backflow assemblies are mechanical devices that may fail over time and require repair or replacement. The USC List of Approved Backflow Prevention Assemblies includes many different manufacturer and model types. The failure rate for the most commonly used devices in Santa Rosa is shown below. 

Calendar Year 2023





Failed (repair/replacement)

One Year Failure Rate (%)































Show All Answers

1. What is a backflow prevention device?
2. How often must a backflow prevention device be tested?
3. I just moved in or rebuilt the property. Why does the backflow prevention device need to be tested?
4. How will I know when it is time to have a backflow prevention device tested?
5. How do I get in touch with a Certified Tester?
6. How much do the testers charge for a backflow test?
7. What happens if I don’t have a passing backflow test for this year?
8. I’m a tenant. Doesn’t my landlord/property manager need to take care of this?
9. My postcard says my last test was less than 12 months ago. Why do I need another test?
10. Can’t I test it myself?
11. How can I make sure my backflow prevention device does not break during a freeze?
12. What is a Backflow Administration Fee?
13. How do I install a backflow prevention device?