What is backflow?

Backflow occurs when water flow is reversed from its intended direction and, by way of a cross connection, is pushed or siphoned back into the drinking water system. Backflow can occur by the following mechanisms:

  • Backsiphonage - The pressure in the drinking water system is lowered. This type of backflow can result from water line flushing, fire fighting, or water main breaks.
  • Backpressure - The pressure in a customer's piping system is greater than that of the drinking water system. This primarily occurs in commercial applications involving pumps, high rise buildings, or boilers.
  • Examples:
    • A garden hose submerged in a bucket of soapy water, hot tub, or swimming pool creates a cross connection. This allows the contaminated water (soapy water or chemically treated hot tub or pool water) to be backsiphoned into the water system.
    • Water containing lawn chemicals is backsiphoned into the water system by way of a lawn irrigation system.

Show All Answers

1. What is backflow?
2. How can cross connections and backflow affect my drinking water?
3. What can I do to prevent backflow?
4. What is a backflow prevention assembly?
5. When is a backflow prevention assembly required?
6. What is a Certified Backflow Assembly Tester and how can I find one?
7. What does it cost to test a backflow prevention assembly?
8. What are some different types of backflow prevention assemblies, devices, and methods?
9. Do I need a permit to have a backflow prevention assembly installed and is there a permit fee?
10. Who can install a backflow prevention assembly?
11. What does it cost to install a backflow prevention assembly?
12. Why am I required to have my backflow prevention assembly tested?
13. How often do backflow assemblies need to be tested?
14. Who is responsible for the testing and maintenance of the backflow prevention assembly?