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Maintaining water quality with hydrant flushing

When we need to clean inside the city’s pipes, we flush water through hydrants. It’s one way we maintain excellent water quality.
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About hydrant flushing

Photo of two workers wearing orange safety vests next to an orange hydrant that has a red hose connected to it and white foamy water gushing out of the hose onto the street.
Water Bureau flushing crews use the unidirectional flushing technique to clean the inside of pipes. Unidirectional flushing is well-planned to move the water in the pipes at high speeds to clean out sediment and maintain water quality.

Hydrant flushing is a technique used across the country to maintain water quality and clean the pipes that deliver water to homes and businesses. In unfiltered water systems, such as Portland’s, sediment and other organic material accumulate at the bottom of the water mains. This material can impact water quality and cause discolored water at the tap if it is stirred up. (Events that could stir up that material include construction, firefighting, and main breaks.) When we flush hydrants, we flush the material out and bring fresh water into the mains.

Water used during flushing is doing important work. While it may look wasteful, the flushing technique the we use is an efficient and necessary use of water to maintain the integrity of the pipes and ensure excellent water quality. Similar to how we brush our teeth every day, the Water Bureau cleans the inside of our water mains on a routine basis. It’s an essential part of, and a planned investment in, maintaining the health of our water system.

Using hydrant flushing, we are currently on track to clean the city’s 2,200 miles of water mains before the new water filtration plant is online in 2027. We want to flush all the mains before then to help prepare the system for a change in water quality and chemistry once the filtration plant is running. After the filtration plant is online, we’ll keep flushing on a continual basis to maintain water quality and drinking water infrastructure.

Our flushing team uses three types of flushing to clean the water main or maintain water quality in an area: autoflushing, spot flushing, and unidirectional flushing.

Flushing in your neighborhood

Find out where is flushing happening in the City on our WaterWorks map

Photo of an orange hydrant with a red box, an autoflusher, attached to it. Next to the hydrant is a white sign that says: Flushing our system to maintain water quality. Water may discharge without warning.
Autoflushers look like red boxes attached to hydrants. The mechanism inside the box is programed to turn on for specific amounts of time. The autoflushers are installed in specific areas to maintain water quality in those neighborhoods.

Flushing usually doesn’t affect Portlanders as they’re going about their day. If you see flushing crews working in your area, please drive carefully and treat them like any other road construction crew.

Flushing crews usually work Monday through Friday, between 8:00 am and 4:00 pm. Every once in a while, circumstances call for crews to work outside these hours.

If there is an autoflusher installed in your neighborhood, they typically run during the night. If you see an autoflusher running during the day, report it by calling 503-823-7525. If you leave a message, please include the intersection where the hydrant and autoflusher are located.

During flushing

Photo of a woman wearing a yellow safety vest next to an orange hydrant that has water flowing out of it. The woman is writing notes on a metal clipboard.
Water Bureau crews use spot flushing as needed to address water quality issues or concerns reported by residents. Crews also use spot flushing proactively to maintain water quality in neighborhoods. Hydrants used for spot flushing may be left on and unattended for a few hours while the flushing is happening.

In rare instances, you might notice discolored water or lower water pressure while we’re flushing. You can report these to the Water Quality Line.

Discolored water is not consistent with the quality of water we intend to serve. If you have discolored water, you may choose to drink bottled water or water from your emergency supplies.

If you have discolored water, you can avoid pulling that water into your whole house’s plumbing. Avoid using tap water or running your washing machine, dishwasher, or ice maker until flushing is complete.

After flushing

If you have discoloration in your water from nearby flushing, run the water at one tap for two to three minutes to see if it clears. If it does not clear, wait an hour and try again. When the water runs clear, run the water at any taps where you had discolored water.

Questions about flushing or want to report discolored water or low pressure? You can report these to the Water Quality Line.