What is Unidirectional Flushing?

Unidirectional Flushing (UDF) is a method of cleaning the water pipes by shutting and opening certain valves and fire hydrants to force the water to flow quickly in one direction. There may be a small drop in pressure or a change in water colour as minerals and sediments get flushed out. This should not affect water service.

Benefits of the UDF program

Slow moving water in the water pipes lets minerals and sediments to build up over time. These deposits can result in water colour and water quality problems and corrode pipes. The UDF program is necessary for:

  • Improving water quality in water mains
  • Reducing bacterial growth
  • Lowering risk of water contamination
  • Improving water colour and clarity
  • Controlling pipe corrosion
  • Helping to restore flow and pressures in system
 Current Progress

The City has made the decision not to run the 2022 UDF program this year. The area planned to be flushed this year will be flushed in 2023.


What Is Unidirectional Flushing (UDF)?

UDF is a method of cleaning the water mainlines through a network of flushing sequences with the water being discharged from a fire hydrant. The UDF program involves closing valves in a specific sequence to create water movement in one direction while opening specific hydrants at the end of that sequence. Maintaining the flushing sequence is important so that the water used in the flushing sequence remains clean. The UDF technique allows higher water flow velocities by isolating certain sections of the water mains. This higher water velocity allows for better scouring of pipes and will use 40% less water in the flushing process than traditional flushing. The flushing of the pipes will dislodge and remove mineral deposits, sediments and biological deposits that accumulate in the water mains.


Why Are We Flushing?

Slow moving water in the water mains allows minerals and sediments to deposit and accumulate over time. These deposits can result in water discoloration and water quality problems and contribute to the corrosion of some of the pipes. A bio-film of micro-organisms can also generate over time in the pipes.


What Are The Benefits Of Flushing?

The benefits include maintaining and potentially improving the water quality, color, and distribution. Flushing reduces bacterial growth, restores disinfectant residual, improves color and turbidity, controls corrosion and can help restore flow and pressures in the water distribution system. A preventative maintenance program can also be implemented on valves and hydrants in conjunction with the flushing program at very little additional cost.


When Will UDF Be Taking Place?

Flushing normally begins in August and can take 2-3 months to complete. However the length of time needed to complete the program and the start date can vary from year to year. Flushing is planned to start in the summer of 2023.


Will You Be Affected?

Flushing will generally occur from 8:00 am until 4:30 pm for most areas. Be aware that a hydrant near you may be opened and used to discharge water into the street for several minutes. There may be a slight drop in pressure or a presence of discoloration from the minerals and sediments that are being flushed out. Water service should not be disrupted during the flushing process. If a discoloration is noticed, please turn the tap off for 15 minutes and flush from your bathtub tap until the water is clear.



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