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Have you ever seen water flowing from a fire hydrant but not a fire in sight? You were probably watching a Unidirectional Flushing (UDF) service.

What is Unidirectional Flushing (UDF)?

UDF simply means guiding water in a single direction through the pipes by systematically closing valves and releasing it through fire hydrants.

How does UDF work?

Most utilities use some form of flushing in a regular maintenance schedule by opening a hydrant in the distribution system and flushing for an extended period of time to move water. The process is known as traditional flushing. Although lots of water is moved, this is not a very effective means for cleaning inside the water mains, as the water is moving from multiple directions at a slower velocity.

UDF, on the other hand, involves the systematic closing of valves and opening of hydrants to create a single direction of flow. All that water flowing in one direction results in faster velocity and more turbulent flow, which means cleaner mains.

We flush from largest mains to smallest mains and the cleanest mains to dirtier mains. This ensures dirty water is not being pushed into clean pipes, and that the pressure stays high.

Why is UDF required?

UDF is effective in:

  • Scouring (scrubbing) of the inside of the pipe.
  • Removing sediment, silt and biofilm.
  • Improving water color.
  • Improving turbidity (clearer water, less cloudy).
  • Increasing chlorine residual.
  • Reducing flushing frequency and water use, which results in savings over traditional flushing.
  • The opportunity for preventative maintenance on water infrastructure.

By pumping high pressured water through the pipes and releasing it through fire hydrants, we rid the mains of biological and mineral deposits and get the cleanest, clearest water to you.

Do I need to do anything?

If you're a residential customer, you can expect temporarily cloudy water or low water pressure for the duration of the flush in your area. Your water won't be turned off and you'll continue to receive uninterrupted water service to your home.

Important: Don't use any type of liquid lawn products that attach directly to your hose when your area is receiving UDF service. Due to the water pressure change, anything attached to your hose could be sucked into it and will end up in your water main, potentially contaminating your and your neighbors' water supply. You can learn more about this hazard on our preventing backflow page.

How long will UDF take?

A drop in water pressure caused by UDF servicing can range anywhere from 15 to 60 minutes, with an average of approximately 25 minutes.

Will UDF servicing increase my water bill?

UDF servicing doesn't affect your water bill. You're only charged for water that passes through your meter and flushed water is emptied out of the distribution system well before then.

Does UDF waste a lot of water?

Because UDF is more effective at getting the pipes clean, we're able to flush less often. And because the pressure and velocity used in UDF is so much higher than traditional flushing, we actually run the water for a shorter duration. Our flushing schedule is also designed to ensure that we never unnecessarily flush an area.

When does UDF occur?

UDF crews work around the clock for about 100 days per year, from May through September. They try to avoid working during the dinner hour peak flushing period.

For more details, view the weekly flushing schedule when it's posted. Please note that the location schedule is confirmed only about a week in advance and can change without notice.

​When does UDF occur?

UDF crews work in the Spring and Fall. They try to avoid working during the dinner hour peak flushing period.

For more details, view the weekly flushing schedule when it's posted. Please note that the location schedule is confirmed only about a week in advance and can change without notice.