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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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Unidirectional Flushing

Unidirectional flushing maintains the water system.

What is unidirectional flushing?

Drinking water systems, especially unfiltered systems like Portland, need to routinely clean the network of pipes to improve water quality. Over time, very fine sediment and organic matter from the Bull Run Watershed settle out of the water and accumulate in the bottom of the pipes. While the sediments are generally harmless, they can make the disinfectant in the water less effective. Additionally, sudden changes in the flow of water can disturb these sediments resulting in discolored water.

The Portland Water Bureau uses three techniques to clean and maintain the drinking water system: spot flushing, autoflushing, and unidirectional flushing.

  • Spot flushing is used when a water quality problem has been identified. This includes when drinking water is discolored due to a disturbance in the system such as construction or other hydrant activity. Portland Water Bureau crews open fire hydrants to flush this water out of the system and bring fresh water into the pipes.
  • Autoflushing is similar to spot flushing and is used to maintain water quality in potential problem areas. This type of flushing uses an automatic flushing device, called an autoflusher, which is connected to hydrants and programmed to flush water at certain time intervals and flow rates. Using an autoflusher reduces the amount of staff time needed to maintain consistently better water quality at certain location in the distribution system, while using water in a more efficient manner.
  • Unidirectional flushing is not used in response to a specific water quality issue but instead is used as routine maintenance to prevent problems from arising. The goal of unidirectional flushing is to scour and clean the insides of the water delivery pipes.  Cleaning the pipes removes sediment that build up in the pipes. This reduces the potential for water quality problems. Unidirectional flushing works by forcing water in the pipes to flow at much higher speeds than normal. Flushing crews first open and close valves to isolate sections of pipe, and then the water and any sediments in the pipes are flushed out through an open fire hydrant.

Improving and Maintaining High-Quality Drinking Water
Unidirectional flushing is used to improve and maintain our high-quality drinking water. Sediments and deposits in the pipes can discolor drinking water. The high speed water flows used in unidirectional flushing is an efficient and cost-effective way to remove sediments and deposits from the pipes and prevent potential water quality issues.

Flushing in Your Neighborhood
Unidirectional flushing will have minimal impacts to customers. If you see hydrant flushing crews working in the area, please drive carefully and treat them like any other road construction crew.

Flushing usually occurs Monday through Friday, between 8 a.m. and 1:30 p.m.

During Flushing
Residents in the immediate vicinity of flushing may notice temporarily discolored water and lower than normal water pressure. The discoloration does not pose a health risk. However, avoid using tap water or running the washing machine or dishwasher until flushing is complete.

After Flushing
If you experience some discoloration in your water from nearby flushing, run the water at one tap for 2-3 minutes to see if it clears.  If it does not clear wait an hour and try again.  When the water runs clear, flush any taps where discolored water was present.


Need Assistance?

The Water Quality Line is available 8:30 am – 4:30 pm Monday-Friday at 503-823-7525 or If you have a discolored water-related emergency after these hours, please call 503-823-4874 option 1 to speak with a Water Bureau Emergency Dispatcher. To learn more about home water quality, visit the Water Bureau’s Drinking Water Quality at Home page.