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The City of Portland, Oregon

Portland Water Bureau

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Customer Service: 503-823-7770


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Backflow Frequently Asked Questions


What is a cross connection?

A cross connection occurs where a private service line pipe connects to a public water main. The most common is a water service feeding into a property at the water meter.

What is backflow?

The water system is designed to flow into properties from the water main pipes to the service line pipes to homes and businesses. Backflow is the unintentional reverse flow of water, allowing contaminants to flow from the service line back into the water main pipe under the street.

How does backflow occur?

Backflow occurs when there is a reverse of pressure in a pipe. For instance, usually the pressure in the water pipes is enough to prevent water from an individual service line flowing back into the water main. But during extreme circumstances, such as a water main break, the loss of pressure in the water main supplying the area can create a backflow. Or, if a business storing used water has a pump that fails, this could result in excess pressure pushing contaminated water back into the main line.

Backflow can also occur within a property, for instance water flowing from a garden hose, back into the water pipe. This can cause a backflow into the structure’s plumbing.

Why is backflow potentially dangerous to public health?

Backflow can be dangerous when it contains contaminants that can be harmful to users. For instance, irrigation sprinkler heads often retract below the surface, into recesses that can collect runoff. This runoff can contain pet waste, fertilizer, or pesticides used to treat the lawn or nearby beds. Once turned off, the pooled water can flow back into the pipe. Without a backflow preventer assembly this water could end up in the water main flowing into neighboring properties.

How do you prevent backflow?

Backflow can be prevented by installing a backflow prevention assembly just behind (property side) the water meter. Smaller backflow preventers can be installed at water spigots, and on other lines inside the property.

What is required when installing a backflow preventer assembly?

Different sizes and types of service lines have different requirements, and the location of a property can also factor into what is required. For instance, the requirements for a high‐pressure fire line are different than those on a relatively small residential line. Lines under 2‐inches are not required to have a backflow preventer assembly, in most cases. Locations on or near water bodies may require a higher level of prevention, as well as locations that house significant quantities of harmful chemicals.

What should I know when hiring a plumber?

When hiring a plumber, we encourage obtaining at least three bids for the work, with references. Ask friends and family for recommendations and read company reviews. Check with the Better Business Bureau before making a hiring decision.

Point of information: Not all plumbers are certified to test backflow preventer assemblies, and not all testers are certified to install a backflow preventer assembly. Be sure that any plumber you hire can do both.

Remember you will need a backflow preventer assembly that is appropriate to the type and size of the service at your property, and your plumber is required to obtain a city plumbing permit for the work.

What to Ask Your Plumber:

  • Is a pressure reducer valve needed for your private service line? (If needed, it can save you from potential damage to your plumbing.)
  • Ask them to check whether your electrical system is or is NOT grounded to your water meter. (If it is, you will need an electrician to properly ground your system for safety.)

What Your Plumber Should Provide You:

  • Final inspection report showing that the final inspection was completed and approved.
  • If you had an electrician properly ground your electrical system, the electrician should also provide you will a final inspection report.

What You Should Give the Portland Water Bureau

Mail copies of your final inspection and testing reports to:

Portland Water Bureau

Attn: Backflow Prevention

1120 SW 5th Avenue, Room B320

Portland, Oregon 97204‐1926,

Include: your name, property address, mailing address if different, email, phone number.

Why is annual testing required?

The State of Oregon requires annual testing of your backflow prevention assembly to insure it is functioning correctly. The results of a test can alert you when work is needed on the assembly, or let you know when it is time to replace it.

Testing is conducted by a certified backflow assembly tester, and the results must be submitted by mail to:

Portland Water Bureau

Attn: Backflow Prevention

1120 SW 5th Avenue, Room B320

Portland, Oregon 97204‐1926,

Include: your name, property address, mailing address if different, email, and phone number.

Contact the Water Quality Inspection Group directly for assistance at 503-823-7480. For records information, please call 503-823-3256.