Backflow is the undesirable reversal of flow of non-potable (untreated) water or other substances through an unprotected service lateral pipe into the water distribution system.

There are two causes of backflow:

  • Back-Siphonage is the reversal of normal flow in a system caused by a vacuum in the supply piping. This can occur if there is an interruption in the water supply due to nearby fire fighting where huge volumes of water are extracted from the water distribution system or, a break in the water distribution system.
  • Backpressure is the reversal of normal flow in a system due to pressure higher than that of the water distribution system pressure. This happens when there is an increase in downstream pressure caused by pumps, temperature increases in boilers, elevated tanks or other pressure-producing systems which may be connected directly or indirectly to the water distribution system.

"cross connection" is a temporary or permanent piping link between a potable (drinking) water system and any source containing non-potable water, chemicals or other substances from which backflow may occur. Examples include a direct pipe connection, such as a service lateral pipe, between the City's water distribution system and an industrial plumbing system, a heating or cooling system, fire suppression system or irrigation system.

Cross connections are classified into three categories:

  • High/Severe Hazards are any cross connection or potential cross connection involving any substances that could be a danger to health. Examples include potential back siphoning or back pressure from chemical plants, food processing plants, hospitals, mortuaries or morgues.
  • Moderate Hazards are any cross connection or potential cross connection that has the probability of becoming a severe hazard. Examples include potential back siphoning or back pressure from high rise apartment buildings, commercial premises, irrigation systems, schools.
  • Minor Hazards are any cross-connection or potential cross-connection that constitutes only a nuisance, with no possibility of any health hazards to the public. Examples include potential back siphoning or back pressure from low-rise apartment buildings, low risk commercial premises, residential homes.

"backflow prevention device" is equipment which, when installed in a piping system, prevents the reversal or backflow of non- potable water or substances. Examples of backflow prevention devices include but are not limited to: reduced pressure principle assembly, pressure vacuum breaker, and double check valve assembly.

The Cross Connection Control Program and amended Water Works By-Law serve to reduce the risk of contamination of the water distribution system through implementation of a plan which would see the installation of a backflow prevention device at the point where the water service pipe enters a building or facility. This process is known as "premise isolation".

The proposed Cross Connection Control Program also addresses the regulation of, and provides for, the installation, maintenance, operation, re-calibration and monitoring of backflow prevention devices in the City Of Cornwall. The program is based on guiding principles as outlined by the Canadian Standards Association (CSA B64.10). The amended Water Works By-law 2016-019

Upon identification of a property which has been classified as a high/severe hazard, these premises will be required to install a backflow prevention device or verify that they have a fully operational backflow prevention device in place within one (1) year of receiving notice to comply. Once all high/severe hazard premises have been addressed, the Cross Connection Control Program Coordinator will turn his/her attention to buildings considered to be moderate hazard premises.

As part of the Cross Connection Control Program, facility operators and/or owners would be responsible to ensure that their backflow prevention devices are inspected and tested annually by a qualified person who is certified to inspect and test backflow prevention devices. Additionally, facility operators and/or owners would be responsible to ensure that a copy of the backflow device test results and associated re-certification documents are forwarded to the City's Cross Connection Control Program Coordinator. Failure to provide such documentation could result in consequences as outlined by the Water Works Bylaw 2016-019. Non compliance could result in fines and/or ultimately, turn off of the water service.


With an effective cross-connection control program, the Cooperation may:

  • increase potable water protection, which reduces risks to public health;
  • reduce the number of backflow incidents;
  • reduce system shut down time and cleanup costs due to backflow incidents;
  • increase consumer confidence and heighten cross-connection control awareness;
  • demonstrate due diligence and regulatory compliance; and
  • reduced liability.



phone icon Contact Us

Municipal Works
1225 Ontario Street, Box 877, Cornwall ON, K6H 5T9

Email this contact
Map this location