What happens during a backflow test, and how often it is required

Before the visit

You receive a confirmed date and time window. We ask for three things in advance:

• where the devices are (mechanical room, meter room, irrigation vault, fire-line room);
• who will let us in;
• whether a brief water shutdown needs to be timed around a tenant, a kitchen or a process.

If you have a notice or last year's report, send it. The device's size, type and serial number let us bring the right kit and the right parts.

The test itself

1. Identify the assembly. The tester records the make, model, size, serial number and location, and checks the tag from the last test.
2. Close the outlet. The shut-off valve after the assembly is closed, which stops the water through it for the length of the test. Where a building has a second assembly in parallel, we test one at a time so the supply stays on.
3. Connect the test kit. Hoses from a calibrated test kit are attached to the assembly's test cocks, the small ports on its body.
4. Run the checks. The exact procedure depends on the device type:
   • Double check valve assembly (DCVA): each check valve is tested to confirm it holds the required differential pressure in the closed direction.
   • Reduced-pressure assembly (RPZ): both checks are tested, and the relief valve is checked to confirm it opens at the required point. The programs require an RPZ, not a DCVA, where the hazard is severe.
   • Pressure vacuum breaker (PVB): the air inlet and the check valve are tested.
5. Record the readings. Pass or fail is set by the limits in CSA B64.10.1.
6. Restore service, tag the device and file. The outlet valve is reopened, and a tag with the date and result goes on the device. The report is submitted to the municipality, for example through Toronto's online form or through Backflow Solutions Inc. (BSI) for Durham. You receive a copy and the filing confirmation.

If the device fails

In our experience a failed test usually means a repair, not a new assembly. The most common cause we see is debris caught between a check valve disc and its seat, which stops the check from sealing. The field note on fouled RPZ checks shows an example. Other causes are worn rubber, a relief valve that does not open, or shut-off valves that do not hold.

You receive a written repair scope. If you approve it, the repair is done, often with a rebuild kit rather than a new device. The assembly is then retested, and the new report is filed.

Toronto: repair within 48 hours of a failed test and retest within 72 hours of the repair. Halton: repair or replace within 96 hours. Durham: report a failure within 24 hours.

How often

The programs on this site require the test, with the exceptions noted:

• when the device is installed (Durham's by-law states only the annual test),
• after it is cleaned, repaired, replaced or serviced, in most programs (Halton sets no retest after a repair; Durham asks for one with a repair notice), and
• at least once a year after that.

What you should keep

Keep the test report, the filing confirmation and any repair invoice. Municipal auditors ask for them, and in our experience insurers and purchasers do too. The report is the fastest way to answer "when was it last tested" without a site visit.

Toronto requires copies of the records submitted to the City to be kept on the property for 7 years. Peel and Durham require test reports to be kept on site for 5 years.