In the Capital Regional District (and throughout much of North
America), every new irrigation system supplied by municipal water is
required to include a device called a "backflow preventer." A lot of
people wonder why they need to have one, and why it has to be tested
regularly to ensure it's working properly (once every 3 years for single
family homes, and once every year for commercial and multi-family
dwellings). The answer is: to protect our shared water supply.
"Backflow" refers to the reversal of the normal flow of water in a
system. In nature, rivers don't get to flow back up, but in a piping
system lots of things can occur that draw water back "upstream" to the
source. A couple of good examples would be a water main being
accidentally damaged by a road crew, or a fire crew hooking up to a
hydrant. The immense amount of water flowing in these situations creates a draw, called "backsiphonage," which sucks water from any nearby piping back into the water main. So any contaminants in the piping of any of the
homes or buildings in the area can be drawn into the water main, to be
shared with the rest of the neighbourhood once the main is repaired.
Irrigation systems present a higher hazard in this regard than household
plumbing, mainly due to the assorted chemicals many people like to
apply to their lawns. These chemicals can easily enter into the sprinkler
system through the sprinkler heads (which tend to draw a little water
back into them every time the system shuts off). Not to mention the
stuff dogs and other animals "apply" to lawns. None of which goes very
well in your morning coffee.
Another type of backflow is "back pressure," where the pressure on the downstream side of things becomes greater than the pressure upstream, and the water reverses flow. This can be caused by a downstream pump, or elevation differences, but is a less common threat than backsiphonage. To learn more about backflow in general, click here.
For most irrigation systems, the CRD requires a type of backflow preventer called a "Double Check Valve Assembly" (DCVA).
These are considered suitable for moderate hazard levels. For any type
of high hazard system where a chemical is being injected into the
water, such as fertilizers at a nursery, or flame retardant in a fire
sprinkler system, a Reduced Pressure Backflow Assembly (RPBA) is required. All RPBAs are tested annually, or more frequently as needed. Testing is done by a BCWWA-certified Cross Connection Control Tester.
A form is submitted to the CRD once the initial test is done, and then
the CRD sends out new forms about a month before the next test is
required.
Backflow events happen all the time, and most go unreported. Click here for a link to a CRD page listing backflow events both local and worldwide. To read the CRD's Bylaw on Cross Connection Control, click here.
Please contact us if you require any backflow testing services, or if you have any questions about
backflow prevention in general.
Best regards,
Mike Isacson, CIC, CID, CIT, CLIA, CIS, CCCT (what do these letters mean? Click
here to find out!)
Owner, Island Waterwise Irrigation