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The City of Portland, Oregon

Portland Water Bureau

From forest to faucet, we deliver the best drinking water in the world.

Customer Service: 503-823-7770


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Cross Connection & Backflow

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The Portland Water Bureau's Water Quality Inspection's Group is involved in the review and approval process of all commercial building plans submitted to the Bureau of Development Services.

Water Quality Inspections staff are able to help in the planning and specifications of any backflow assembly installation a project may require.

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

What is Backflow?
Backflow takes place when water flows opposite of its intended direction. There are two conditions that can cause backflow.  It may occur due to either backsiphonage or backpressure in the water system. Backflow can take place within any water distribution system whether it is private or public.

What are Cross Connections?
A cross connection is a physical connection between a potable water supply line and a non-potable source (i.e. chemical process water, ponds, lakes or rivers). Under a backflow condition, connections to non-potable sources could potentially cause contamination of our drinking water.  Cross connections can jeopardize the safety of our drinking water. A hazardous backflow incident can occur through cross connections when backpressure or backsiphonage conditions exist.

Backsiphonage and Backpressure Cause Backflow:  

  • Backsiphonage can occur when a water main or plumbing system in a building loses water pressure, thus creating a reduced pressure in the water supply piping. This reduced pressure will allow the direction of the water in the system to flow opposite of the normal direction of flow. Such pressure differences can cause siphoning of non-potable water and other liquids back into the potable water lines.
  • Backpressure occurs when water pressure in a building or fixture becomes greater than the water pressure in the water supply piping. This condition can force non-potable water or other fluids back into the potable water system.