Backflow is a term which is used to describe water which is flowing in a direction contrary to the intended ‘normal’direction of flow within or from a water fitting. This may be caused by either back siphon-age; a system condition where there is a sudden interruption of a supply to a property, thus creating a vacuum in the pipework or backpressure; where the incoming pressure from the supply is less than the pressure within the plumbing system.

As protection of drinking water is vital to public health, water regulations stipulate that backflow prevention devices should be fitted to plumbing system to ensure that, even if backpressure or back siphon-age occur, the water supply will not be contaminated as a result.