What is Plumbing Back-flow?

Back-flow occurs when wastewater (sewage, grey water, etc.) develops a reverse flow (opposite to design) and enters a potable (drinking) water source within the same system. Most often caused by a drop in the pressure of a structure’s water supply, creating a negative supply pressure. Ranging from being a nuisance to being potentially hazardous and even life-threatening, back-flow must be resolved as soon as it is detected. The expert professionals at Burnaby Plumbing have the resources available to diagnose and repair a back-flow problem.


As the most common cause of back-flow in a plumbing system, back-siphoning is created by a sudden drop in the supply pressure of a water main. This happens when there is an extremely high demand is placed on the potable water supply:

  • when a water main breaks
  • when a hydrant is opened by firefighters
This high demand on supply pressure causes a significant drop in water pressure which in turn can cause a siphoning  effect. As a result, wastewater is siphoned into the potable water supply of local structures (homes, businesses, etc.).

When there is a connection between potable water and any other liquid (wastewater, other hazardous liquids). If this connection can potentially cause the contamination of a potable water system through back-flow, it is called cross-connection. A real-world example of cross-connection is when potable water is used to flush the wastewater system. A significant drop in the potable water supply pressure can cause back-siponage through a cross-connection, contaminating your drinking water:

  • when a water main breaks
  • when a hydrant is opened by firefighters
  • water main repairs that require the valve be closed
  • Hydrant flushing
Back-Flow Prevention
Burnaby Plumbing can install a back-flow prevention valve that will eliminate the potential for potable water contamination. The back-flow prevention valve is essentially a check valve installed at the water supply line prior to entering or just after entering your home. This valve is positioned such that it closes when a negative pressure exists in the water supply main, keeping contaminants from flowing into the potable water system and not allowing potable water to flow back into the main supply line. A back-flow prevention valve will insure that your family’s potable water is never contaminated with bacteria, sewage and other potentially harmful toxins.