Cross Connection Control

What is a cross connection

Any existing or potential connection to a potable water system that could allow harmful or unwanted substances into the system.

Causes of backflow

Backsiphonage and backpressure are the two causes of backflow conditions. Backsiphonage occurs when the supply pressure drops below the static head pressure in the system (building). An example of backsiphonage could be:

Your filling your above ground pool with the hose stuck inside the pool and a water main breaks down the road from your home. Your supply pressure drops to zero and because the water main is lower than your pool it could siphon though your plumbing system to the area of lower pressure. The hose in the pool is a cross connection and could have been prevented with a hose bib vacuum breaker.

Backpressure can cause backflow into a potable water system when it is connected to a non potable source that is capable of creating its own pressure by means of a pump, thermal expansion or head pressure. One example of backflow caused by backpressure could be:

 A boiler has a malfunctioning backflow preventer on the make-up water. If the potable water system was shut off and drained the pressure from the boiler could cause treated water to be forced into the potable system.