Backflow preventers protect the municipal drinking water supply from contamination caused by reverse flow — water flowing backward from a building's plumbing into the public water main during pressure drops or back-pressure events.

Double Check Valve Assemblies (DCVA) for low-to-medium hazard applications, and Reduced Pressure Zone (RPZ) assemblies for high-hazard applications (boilers, irrigation with chemicals, healthcare equipment, food processing). The hazard level determines the required device type.

Annual testing is required by most Ontario municipalities. Test reports must be submitted to the local water authority within the required timeframe — typically within 30 days of testing. Contact your municipality for your specific deadline.

Certified backflow prevention testers recognized by Ontario municipalities (typically OWWA-certified). Testers must use calibrated equipment and provide a standard test report submitted to the municipal water authority.

The device must be repaired or replaced and retested before the municipality's deadline. Some municipalities allow a short grace period; others may issue compliance orders for delayed repair. Repair promptly and keep the pass test report on file.

Most Ontario municipalities with cross-connection control programs require backflow prevention on all commercial water service connections. The OBC also requires appropriate backflow protection regardless of whether a municipal program exists.

Immediately after the water meter inside the building — in the mechanical room or near the water service entry. Secondary devices may be installed at boiler connections, irrigation connections, backflow prevention connections, and other high-hazard internal connections.

Contact your local municipality's public works or water services department. In Toronto, contact Toronto Water; in Mississauga and Brampton, their respective public works departments. Your backflow testing contractor can also confirm the requirements for your municipality.