Backflow is when water which could be contaminated, is flown in the opposite direction and drawn back into the plumbing system.
Causes of backflow
- Back pressure
Back pressure can occur, for example, in an unvented heating system where the water heats up and expands.
- Back siphonage
Back siphonage happens when the pressure in the supply is lower than the pressure in the plumbing system. For example when a pool, a toilet cistern or a sink is placed higher than the hose (the supply point), the water can start the flow the other way.
Air gaps or check valves to prevent backflow
- Simply add an air gap between the water supply outlet and the highest water level of an appliance (taps on sinks, wash hand basins, toilet cisterns).
- If an air gap cannot be installed, use a single or double check valve
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