Backflow Prevention

Woman filling glass with water from tap in kitchen, closeup

McMinnville Water & Light is committed to providing you with clean, safe drinking water.

Although the water that reaches your home is safe and of the highest quality, contamination can occur within your own piping system. The goal of our Backflow Prevention Program is to protect McMinnville’s drinking water supply from pollution or contamination by keeping water that has entered a facility or home from flowing back into the public water system.

This is where you can help. With an understanding of the hazards associated with cross connections and backflow, you can help us protect our drinking water.

For information on Oregon State regulations, visit the Oregon Heath Authority website.

What is Backflow?

Water systems depend on water pressure to keep water flowing in the proper direction through the pipes. 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.

What is a Cross Connection?

A cross connection is a connection between drinking water and other water or fluids of unknown quality. Examples include lawn irrigation, boilers, wells, fire sprinkler systems, and swimming pools or hot tubs that are hard piped for filling purposes. To prevent cross connection, backflow preventers are installed to stop the backflow of contaminated water into the drinkable water supply.

How Often Do Backflow Assemblies Need to be Tested?

Like any mechanical device, a backflow prevention assembly is subject to failure. The State of Oregon requires that all assemblies be tested once each year by a certified tester. Annual testing ensures that assemblies are operating as designed. They must also be tested at the time of installation, after repairs and after relocation.

Lawn Irrigation Systems

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:

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

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.

View descriptions of the PVB, DC, and AVB (PDF).

More Resources:

McMinnville Water & Light Cross Connection Control Policy (PDF)
Chapter 333 – State of Oregon Regulations
McMinnville Water & Light Backflow Brochure (PDF)

If you have any questions concerning certified testers, backflow installations, or approved backflow prevention assemblies please call us at (503) 472-6919, ext. 5.