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Waterwise Blog: The Basics of Backflow

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

 

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