Water Main Cleaning

Water Main Cleaning

General Information

As part of our ongoing commitment to safe drinking water the City of St. John's Water and Wastewater Division normally conducts a unidirectional water main flushing program from May to October.  This maintenance activity ensures we continue to provide the highest quality drinking water within our water distribution network.

The flushing generally occurs from 8 a.m. to 4 p.m. for most areas. There may be a slight drop in pressure or a presence of discoloration from the minerals and sediments that are being flushed out of the system. Service should not be disrupted during the flushing process. Areas being affected by the flushing process will have flushing signs placed throughout each neighbourhood as a reminder. We urge all residents to use caution while traveling around the Environmental Services personnel and while entering areas of water accumulation during this program.

Frequently Asked Questions

  1. What is unidirectional water main flushing?
  2. What is conventional water main flushing?
  3. Are there other benefits to using the unidirectional flushing technique?
  4. When will you flush the water mains?
  5. How long does it take to flush the water mains on each street?
  6. How will I know when you are cleaning the water mains on my street? 
  7. How will I be affected during the hydrant flushing program?
  8. Can I use my water when you are flushing the water mains in my neighbourhood? 
  9. Will I notice anything different about my water after you have cleaned the water mains? 
  10. How can I clear up the water?
  11. What should I do if the water is still discoloured after three to four hours?
  12. Can I drink the water when it is discoloured? 
  13. Why can't you clean the water mains at night?
  14. Is hydrant flushing a waste of water?
  15. Do other cities have similar water main cleaning programs?

What is unidirectional water main flushing?
Unidirectional flushing is a method of cleaning water mains through a network of flushing sequences with the water being discharged from a fire hydrant. This program will involve closing valves in a specific sequence to create water movement in one direction while opening specific hydrants at the end of each sequence. This type of flushing increases the speed of the water flow in the water main, which produces a scouring action and the removal of sediment deposits. The flushing starts at a clean water source (the water treatment plant for example) and moves towards the outer limits of the City. This ensures that clean water is always used to flush the mains.
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What is conventional water main flushing?
In conventional flushing, the water used to flush the main does not always begin at the clean water source (such as the water treatment plant) and the speed of the water is much lower than during unidirectional flushing. As a result, more water is required to thoroughly clean the water mains.
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Are there other benefits to using the unidirectional flushing technique?
Yes, in addition to removing more sediment and using less water than conventional flushing, unidirectional flushing tests and exercises the water system valves and hydrants.
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When will you flush the water mains?
We will flush water mains in different areas of the City each year, starting in May and ending in October from 8 a.m. to 4 p.m., Monday to Friday.
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How long does it take to flush the water mains on each street?
It takes about 30 to 60 minutes to flush the water mains on each street. After the flushing, the water can be cloudy for up to four hours.
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How will I know when you are cleaning the water mains on my street? 
The City will inform residents before starting the unidirectional flushing program by posting notices on our website and placing advertisements in the local newspaper. In addition we will place signs in your neighborhood advising of the hydrant flushing.
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How will I be affected during the hydrant flushing program?
You probably will not even be aware that flushing is taking place in your neighbourhood. Flushing is generally conducted between 8 a.m. and 4 p.m., Monday through Friday. Select hydrants will be opened for water pipe flushing. While the hydrants are open, the residents in the neighbourhood may experience discoloured water or a small drop in water pressure, however, your water service should not be interrupted. If you have no water pressure please notify Access St. John's at 311 or (709) 754-CITY (2489), as soon as possible.
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Can I use my water when you are flushing the water mains in my neighbourhood? 
When you see flushing being carried out on your street, you should avoid using water for any purposes that require clean water, such as preparing food and beverages, medical and dental procedures, or laundry. You should also avoid using your hot water system to minimize the amount of sediment drawn into your hot water tank.
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Will I notice anything different about my water after you have cleaned the water mains? 
Water is sometimes discoloured, milky or cloudy looking or has a chlorine smell after water main cleaning, but this should not last long.

Discoloured Water
The flushing process is designed to clean the water mains and will cause discoloured water, but this should not last long. You should avoid laundering clothing to minimize staining.

Cloudy Water
Water is cloudy when air gets in it and makes tiny bubbles. These bubbles are harmless and will disappear if you let the water sit for a few minutes.

Chlorine Smell
We add enough chlorine to the water to keep it safe. You can easily get rid of the chlorine taste and smell by filling a container with water and keeping it in the fridge for drinking - much of the chlorine will leave the water overnight.

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How can I clear up the water?

  • Turn on a cold water tap and let the water run for a few minutes, we recommend using the cold water faucet on a bathtub. Do not choose a tap that has a water filter connected to it, or the sediment may clog your filter. Do not use a hot water tap because it could draw sediment into your hot water tank.
  • Catch some water in a light-coloured cup or container to see if it is clear. You can use your water if it is clear.
  • If the water does not clear in 15 minutes, wait 30 minutes and try again.

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What should I do if the water is still discoloured after three to four hours?
If this happens, please call Access St. John's at 311 or (709) 754-CITY (2489) and a City representative will contact you.
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Can I drink the water when it is discoloured? 
If the water is discoloured, we recommend that you boil the water before drinking it.
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Why can't you clean the water mains at night?
It is safer for staff to work on the streets in daylight. Also, it is easier in the daylight to see when all the sediment has been flushed out and the water is running clear.
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Is hydrant flushing a waste of water?
No, the amount and cost of water used in flushing is a small price to pay compared to the benefits of assuring the quality of your water and maintaining our infrastructure.
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Do other cities have similar water main cleaning programs?
Yes, many cities have some type of flushing program to clean their water mains (either conventional flushing or unidirectional flushing). This is considered the best way to improve water quality and increase the reliability of the water distribution system.
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For additional help, contact information or to submit a request visit Access 311.