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The reversal of the normal direction of the flow of water.

Backflow preventer device:

A device that prevents backflow.

Backflow prevention device tester:

a person who is certified to perform backflow preventer testing by an accredited organization recognized by the regulatory authority.


Any actual or potential connection between a potable water system and any source of pollution or contamination.

Note: Bypass arrangements, jumper connections, removable sections, swivel or changeover devices, or any other temporary or permanent connecting arrangements through which backflow can occur are considered cross connections.


Any person, firm or company controlling a property subject to this regulation.

Potable or drinking water:

Water safe for human consumption.

Question: What is “backflow prevention”? 

Answer: Backflow prevention, is a plumbing strategy aims at averting the flow of contaminated water into a drinking water supply.

Question: What is a cross-connection? 

Answer : Any actual or potential connections like bypass arrangements, jumper connections, removable sections, swivel and changeover devices or any other connection, permanent or temporary, between a potable water system and any source of polluted or contaminated water. Such systems create situations where backflow is possible. Even an outdoor garden hose that feeds an irrigation system could pose a hazard.

Question: What are the most common causes of contamination of drinking water?

Answer: a) Back siphoning: the reversal of the normal flow of water caused by a depression in the supply system and b) Back pressure: the reversal of the normal flow of water caused by a pressure higher than the supply pressure.

Question: What are the causes of back siphoning ?

Answer : Back siphoning can be caused by an anomaly in the public water supply system such as an interruption of service, broken pipes, the use of numerous fire hydrants, or any other external devices.

Question: What are the causes of  back pressure? 

Answer : A back pressure can occur when the pressure downstream is greater than the pressure upstream. For example, when a circulation system or a pump is used in a heating or sprinkler system, there is a simultaneous drop in pressure in the public water supply. As a result, the high pressure generated by the pump can reverse the normal flow of water.

Question: When I turn on the water supply system after a field test, should I pressurize the backflow preventer device or supply the piping first?

Answer : To avoid water hammer, you must first pressurize the backflow preventer device, then supply the piping by slowly opening the stopcock #2.

Question: True or false? I installed a backflow prevention device at the main water entrance of the building. So now my work is done. I protected the city’s public waterworks from contamination due to backflow. 

Answer : False. The backflow prevention device installed at the main water source protects the public waterworks from backflow, HOWEVER cross-connections inside the building must also be protected with an appropriate device.

Question: True or false? After completing repairs on the backflow prevention device, there is no need to test the device since testing is only required on an annual basis.

Answer : False. A backflow prevention device must be field tested in EACH of the following cases and BEFORE turning the water back on:

  • Upon installation
  • When relocated to another location in the system
  • After changes to the supply piping
  • After every maintenance including cleaning,
  • After it has been repaired
  • At least once a year 

Question: Can I use the #1 shut-off valve of a backflow prevention device as a main shut-off valve for the entire building?

Answer : No, the purpose of the #1 shut-off valve of a backflow prevention device is for the tester to properly field test the device. A main shut-off valve must be installed on the main water connection of the building, in accordance with section 6.1.3 of the Canadian National Plumbing Code.

Question: I am currently doing a backpressure test on the #2 check valve of a reduced pressure assembly (RP). The relief valve is open and water flows constantly. What does that mean?

Answer : The check valve #2 is not watertight; check for leakage.

Question: Without doing any tests, the relief valve of a reduce pressure device opens and closes from time to time. What are the causes?

Answer : Sudden pressure fluctuations in the supply piping upstream of the device can cause the relief valve to open sporadically.

Question: When testing the opening of the relief valve of a reduced pressure assembly, I noticed that I have to open the low-pressure valve of my gauge more than one-quarter turn. What does this mean?”

Answer : There is a leak in the # 2 shut-off valve because water is still flowing inside the device.

Question: Which valves of the differential pressure gauge must be opened to test the #2 check valve of a reduced pressure assembly.

Answer : The high pressure and by-pass valves.

Question: True or false? Another way to test the opening of a relief valve is to close the #1 and #2 shut-off valves and open test cock # 2. Water should then flow from the relief valve.

Answer : True. The water in the device is static. By opening test cock #2, the water pressure upstream of the relief valve is reduced. The reduced pressure area will then have a higher pressure and water will flow out.

Question: True or false? The # 2 shut-off valve is closed but before I can start my test, water is pouring from the relief valve. It is probably due to leakage on the # 1 check valve.

Answer : True. If check valve # 1 leaks, the pressure of the zone upstream of the relief valve and the pressure of the reduced pressure zone will become equal, which will inevitably cause the relief valve port to open.

Question: I am testing the #1 check valve of a DCVA on normal flow and my gauge reads 0 psig. What does that mean?

Answer : A failure of the # 1 check valve.

Question: While testing backpressure of the # 1 check valve of a DCVA, I usually slightly loosen the low-pressure hose plugged on the # 2 test cock. Is it a good idea? Why does the pressure climb when I do this?

Answer : Loosening the low pressure hose will cause water to flow from the backflow preventer upstream of check valve # 1, which will increase the pressure differential across the valve. As the differential pressure increases at the gauge dial, it becomes easier to take a reading and confirm the sealing of the valve.

Question: True or false? While testing the check valve of a pressure vacuum breaker, the flexible hose of the gauge should be plugged on the # 2 test cock.

Answer : False: on the #1 test cock.

True or false? The atmospheric vent of a pressure vacuum breaker must be completely opened before the pressure at the gauge reaches 1 psig?

Answer : True, that is the minimum set point, and complies with CSA B64.10 standards.

Question: Water is pouring from the atmospheric vent of a pressure vacuum breaker before I can even do any tests. What does that mean?

Answer : A failure of the atmospheric vent.