Backflow prevention

Backflow prevention program

Purpose of the program

In order to help ensure the supply of safe, clean drinking water to its users, the City of Guelph has chosen to take a pro-active approach with respect to backflow prevention. This has resulted in the establishment of a Backflow Prevention Program designed to:

  • enhance Backflow Prevention Regulations in the City’s Water By-law (1991)-13791
  • identify any and all cross-connections where potential contamination of potable water may occur
  • maintain a database of qualified backflow device testers
  • maintain a database of water users who have backflow prevention devices.


Backflow means the flowing back of or reversal of the normal direction of flow of water;

Backflow Prevention Device means a device that prevents backflow and includes a reduced pressure principle assembly, dual check valve, double check valve and the like;

Cross-connection means any actual or potential connection between a potable water supply or system and any source of pollution or contamination and includes any by-pass, jumper connection, removable section of pipe, swivel or changeover device and any other temporary connecting arrangement through which backflow may occur.


Backflow prevention ensures that potable water is protected against the entry of contaminants, pollutants, infectious agents or other materials or substances. This is achieved through the installation of an appropriate backflow prevention device at the water connection where this potential exists. The main water supply must also be isolated by installing a backflow prevention device at or near the meter.

Backflow occurs as a result of either back siphonage, back pressure or both. Back siphonage is a reversal of normal water flow in a system caused by a negative pressure in the water line. Back siphonage is induced when there is a reduction in, or stoppage of, the main water supply pressure due to nearby fire fighting, repairs or breaks in watermains. Backflow can also occur when there is an increase in the downstream water pressure above that of the supplied water pressure (back pressure) or, when there is a direct cross-connection between the potable water supply and another process line which has the potential to transmit a contaminant into the potable supply.

While the possibility of such events occurring and contaminating potable water supplies may seem like an industrial or institutional problem, backflow can occur in any water supply line including individual residential units. The potential for contamination and fatal illness due to accidental poisoning does exist in every home. Therefore there is a need to raise awareness of this issue with all residential, as well as, all industrial, commercial and institutional water customers in Guelph.

Backflow permit requirements


To ensure installation complies with the Ontario Building Code and all other relevant codes and by-laws.

When do I need a permit?

  • Installing a new or additional device,
  • Replacing a device that is not identical to the one being replaced (different type, size, location or used for different purpose. If you are replacing a device that is identical, no permit is required).

What information is required?

  • Estimated cost of instalment
  • Name, address, telephone numbers of owner and contractor
  • Size, type and purpose of each device

How do I get a permit and book inspections?

Building permit applications are required to be submitted electronically. You can apply for a permit and book inspections through the Guelph Permit and Application System. Please allow 48 hours’ notice for inspections.

Documents and forms

Instructions For Annual Testing and Resurvey

Backflow Prevention Device Test Report

Backflow Prevention Device Removal Form

Cross Connection Control Survey

Cross Connection Control Survey Form – General

Appendix A

Appendix B – Dental Office

Appendix C – Restaurant

Appendix D – Mortuary

Appendix E – Hospital

Can’t find what you need?

Use this form to send us a question. We’ll put you in touch with a team.

For more information

Jeff Crossman
Backflow Prevention Officer
Building Services
519-837-5615 extension 2725
[email protected]
Donna Palmer-Hurst
Backflow Prevention Program Coordinator
Building Services
519-837-5615 extension 2642
[email protected]