The City of Toronto ensures that residents, businesses, and visitors have access to clean, safe drinking water. To meet this need, the city has a water supply by-law, which defines the roles and responsibilities of both property owners and the City to protect the integrity of the water supply system.

Part of this by-law is the backflow prevention program, which is a set of regulations that outlines the types of properties that need to take measures to prevent backflow from entering the local water supply, the measures that they must take, and the penalties for non-compliance.

Buildings on the University of Toronto campus fall under the types of properties that must prevent backflow from entering the local water supply. So, U of T has backflow prevention devices installed on its water supply lines to prevent harmful chemicals, toxins, and foreign material from entering the city of Toronto’s clean drinking supply.

Facilities & Services has a robust program in place to test backflow preventers on the St. George campus to ensure proper operation. As part of the city’s backflow prevention program, F&S must report back to the city about many of the backflow preventers on campus.

Backflow

Backflow is a flowing back of water or reversal of the normal direction of flow. This can be caused by back siphonage or back pressure.

Types of backflow

Back siphonage

Back siphonage is backflow caused by negative pressure, such as from a vacuum, in a public water system. The effect is like drinking water through a straw. Back siphonage can occur when there is a stoppage of the water supply.

Back pressure

Back pressure is a pressure that is greater than the municipal water system supply pressure. It can happen when there is a connection to a non-potable supply operating at a higher pressure than the water distribution system. Increases in pressure can be created by booster pumps, temperature increases in boilers, interconnections with systems operating at higher pressures, and elevated piping.

Backflow preventers

A backflow preventer is a device that is installed on a water pipe that allows water to flow in one direction and prevents it from flowing in the opposite direction. The purpose of this device is to prevent drinking water from being contaminated by other sources because of backflow, which can cause serious health problems. Some types of backflow preventers require testing to ensure that they work as intended.

Plumbing codes mandate that drinking water be protected against backflow at all cross-connections between a drinking water system and any potential source of contamination.

Types of backflow preventers

There are many types of backflow prevention devices: double check valve assembly and reduced pressure principle assembly. The type of backflow prevention device required in a building is based on the hazard level from Toronto’s municipal code and the kinds of work that take place within the building.

Double check valve assembly

This assembly has two check valves arranged in a series. This means that if one valve fails, the other can still prevent backflow. It works to prevent both back siphonage and back pressure in situations that are categorized as minor to moderate risk. This assembly must be tested at least once a year to ensure proper operation.

Reduced pressure principle assembly

This assembly has two independent check valves that are arranged with a reduced pressure zone in between them. If one begins to leak, it will discharge water from the relief port. Because there is a potential for discharge, these devices need to be installed with the relief port piped to the drain. This assembly is designed to prevent backflow caused by back siphonage and back pressure. It is designed for high-risk applications.

Pressure vacuum breakers

These are designed to protect against a non-health hazard, such as a pollutant, or a health hazard, such as a contaminant, under a back-siphonage condition only. They consist of an independently operating internally loaded check valve and an independently operating loaded air inlet valve located on the discharge side of the check valve.

Testing

Along with installing the appropriate backflow prevention devices, the water supply by-law also requires F&S to perform regular maintenance, test the devices, and get regular backflow prevention device surveys. F&S must also keep records about the surveys, testing, and maintenance of backflow devices.

Backflow prevention devices must be tested:

• at the time of initial installation; and
• within 72 hours after a device has been cleaned, repaired, replaced, serviced, or overhauled; and
• at least once a year.

F&S plumbers, and fire system sprinkler fitters certified as cross-connection control specialists complete the backflow preventer testing. During the test, they switch off the downstream shut-off valve and wait a few minutes before linking up test kit hoses to check the incoming pressure from the city water supply. They look to see if check valves one and two close tightly when there’s back pressure. If the device is a reduced pressure type backflow preventer, the relief port discharges water with a difference greater than 2 PSI. They then report the results of the test to the city.

Minimizing impact on building occupants

Our regular testing of backflow prevention devices is critical to maintaining a reliable and safe environment for members of the U of T community and the City of Toronto.

In buildings with more than one backflow preventer on domestic water systems, there is no impact on occupants.

In buildings with only one backflow preventer on the domestic water system, the cross-connection control specialist must turn off the water for the first test which usually takes less than five minutes.

U of T has six buildings that have one backflow preventer on the domestic water system:

• Enrolment Services (127)
• Faculty of Law (040)
• Goldring Centre for High Performance Sport (042)
• Innis College (132)
• Munk School of Global Affairs (012)
• Myhal Centre for Engineering Innovation and Entrepreneurship (087)
• New College III (131)
• Varsity Pavilion (041)

At these buildings, F&S tries to schedule the testing to happen early in the morning (before 6 AM) or late at night (after 11 PM) to avoid impacting occupants.

F&S carefully plans, schedules, and notifies our campus partners via service alerts about water shutoffs to minimize the impact on operations, research, teaching, and other campus activities.