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Do You Need a Backflow Preventer in Ontario?

Updated: Oct 4, 2023

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If you own or operate a property in Ontario that falls under the categories of industrial, commercial, institutional, or Part 3 residential (as defined by the Ontario Building Code), you are required by law to install a backflow prevention device on your water supply line. This is to protect the safety and quality of the drinking water in the City’s water distribution system from potential contamination.


But what is backflow and how can it affect your water quality? In this blog post, we will explain what backflow is, how it can occur, and how a backflow preventer can prevent it.

Image from Indiana Backflow

What is Backflow?

Backflow is the undesired reversal of water flow against the normal direction. This can occur through two mechanisms: back siphonage or back pressure.


Back Siphonage

Back siphonage is backflow caused by a negative pressure (i.e., a vacuum or partial vacuum) in the public water system. The effect is similar to drinking water through a straw. Back siphonage can occur when there is:

1. A stoppage of water supply due to nearby break in a water main.

2. Line repair or break that is lower than a service point.

3. Lowered main pressure due to high water withdrawal rate such as fire hydrant use or water main flushing.

4. Reduced supply pressure on the suction side of the booster pump.


When back siphonage occurs, contaminated water from your private water system can be pulled into the City’s distribution system, posing a health risk to consumers drinking water from the system. For example, if you have a hose connected to a faucet and submerged in a bucket of dirty water, and there is a sudden drop in water pressure in the City’s system, the dirty water can be siphoned back into your faucet and into the City’s pipes therefore passing it into someone else's property and drinking water.


Back Pressure

Back pressure is backflow caused by a positive pressure (i.e., higher than atmospheric) in a private water system that is greater than pressure in the City’s water supply system. This can result in water from the private system forcing its way into the City’s distribution system. Back pressure can be caused by pumps, elevated tanks, temperature increases in boiler systems, and other local pressure events.

When back pressure occurs, contaminated water from your private water system can be pushed into the City’s distribution system, posing a health risk to consumers drinking water from the system. For example, if you have a boiler that heats water to a higher temperature than the City’s supply, and there is a malfunction in the boiler’s pressure relief valve, the hot water can flow back into your faucet and into the City’s pipes.

Backflow preventer diagram courtesy of the Bloomington Indiana Government page.

How to Prevent Backflow

The basic mechanism for preventing backflow is a mechanical backflow preventer, which provides a physical barrier to backflow. The principal types of mechanical backflow preventer are testable devices such as the reduced-pressure principle assembly (RP), the pressure vacuum breaker assembly (PVB), and the double check valve assembly (DCVA).

The type of backflow preventer required for your property depends on the hazard level of your facility, which is listed by sector in Schedule 5 of the Water Supply By-law. For example, facilities classified as “severe hazard” require an RP device, while facilities classified as “moderate hazard” require a DCVA device.

A backflow preventer must be installed by a plumber licensed with the City of Toronto. You can obtain a list of qualified plumbers by sending a request to backflow@toronto.ca. A backflow preventer must also be tested at least once a year by a certified cross connection control specialist to ensure proper operation. You can submit your test report online through the City’s website.


Conclusion

Backflow prevention is an important measure to protect the safety and quality of the drinking water in Ontario. By installing and maintaining a backflow preventer on your property, you are complying with the law and helping to prevent contamination of the City’s water distribution system. For more information on backflow prevention, please visit owwa.ca or contact Toronto Water at 416-394-8888.



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