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The City of Portland, Oregon

Portland Water Bureau

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Flushing: Using Water Wisely to Maintain Portland’s Water Quality


Customers may encounter a running hydrant or valve with a flushing sign or a Portland Water Bureau barrier and naturally think it is just a waste of water.

In fact, crews are flushing the system, an important tool to maintain water quality, especially in the summer when warmer water can lead to water quality issues.

This summer much of the Northwest is experiencing drier than normal conditions with some areas facing water shortages. However, Portland is not facing water shortages, and is fortunate in that we have two sources of water to meet Portland’s needs. We are constantly monitoring our water resources and balancing maintenance activities with available supply.

Water crews routinely monitor flushes to use the right amount of water needed to maintain water quality, and deliver clean, cold, constant water to our customers.

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

  • Spot flushing is used to flush lower quality water from the system and bring in fresh higher quality water. This includes drinking water that is discolored due to a disturbance in the system such as construction or other hydrant activity. Spot flushing is also used to flush out dead-ends or low-use areas in the system. Portland Water Bureau crews open fire hydrants to flush this water out of the system, monitoring the flush to know when water quality has improved and ensuring water is used wisely.
  • 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 builds 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.

For more information, visit the following Portland Water Bureau webpages:


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