Backflow Prevention

Cross Connection and Backflow Prevention

The Basics

What is Backflow?

Water systems depend on water pressure to keep water flowing in the proper direction from the source through the pipes to your tap. However, anything that causes a drop in water pressure, such as a water main break or heavy use during a fire, can create a reverse flow from the customer’s plumbing system back into the public water system. This is called backflow.

Backflow can also occur when the customer’s water system has a higher pressure than the public water system. The water flowing backward could contain something that might contaminate the drinking water supply.

What is a Cross Connection?

A cross connection is a connection between drinking water (also known as potable water) and other water or fluids of unknown quality (also known as non-potable water).

To prevent against cross connection, backflow preventers are installed to stop the backflow of contaminated water into the drinkable water supply.

What Are Some Common Cross Connections?

Examples of common cross connections that require backflow protection:

Fire sprinkler systems Properties having water wells
Lawn irrigation systems Boiler units
Swimming pools, spas, and hot tubs Hospitals and Medical Clinics
Utility sinks with threaded faucets Industrial facilities
Fertilizer injection equipment  Beverage machines using carbon dioxide

Backflow Prevention Assemblies and Installation

What Are the Standards For Backflow Assembly Installation?

McMinnville Water and Light Installation Specifications can be found here.

What Is Required For A Lawn Irrigation System?

If you are planning to install a lawn irrigation system, please be aware that all irrigation systems must have approved backflow protection. A permit is also required, and is obtained through the City of McMinnville Building Division, 231 NE 5th Street, McMinnville.

The following State approved backflow assemblies are allowed for installation on a lawn sprinkler system per the City of McMinnville and McMinnville Water & Light standards:

  • Pressure Vacuum Breaker Assembly (PVB)
  • Double Check Valve Assembly (DC)
  • Reduced Pressure Backflow Assembly (RP)
  • Atmospheric Vacuum Breaker (AVB)

The RP will be the only option available, if installing a lawn irrigation system with chemical injection capabilities.

The PVB, DC and RP must be tested by a Certified Backflow Tester upon installation and yearly thereafter. The AVB is the only backflow prevention device that does not require annual testing; however, it must be inspected by the City of McMinnville and meet all installation requirements.

A description of the PVBA, DCVA, and AVB can be found here.

What Do Backflow Assemblies Look Like?

Pictures of different backflow assemblies can be seen here (download pdf).


What Are The Annual Testing Requirements?

Per Oregon Administrative Rule (OAR) 333-061-0070 and McMinnville Water and Light Policy, all approved backflow prevention assemblies must be maintained and tested at least annually to protect the public water system.

Who Can Test?

Backflow assemblies must be inspected once a year by a certified backflow tester to ensure proper operation. A list of testers who test in McMinnville can be found here.  The assembly must function properly to pass the test.

Laboratory tests on all approved backflow prevention assemblies indicate that some components may fail in time, and periodic testing is the only method to ensure that the backflow prevention assembly is functioning properly and protecting the public water system.

More Resources

Contact Us

If you have any questions concerning certified testers, backflow installations, or approved backflow prevention assemblies please call us at (503) 435-3118.