Questions often arise on the need for backflow prevention devices on water spigots in food establishments. Backflow occurs when non-potable water is pulled into the potable water via a cross-connection - is a physical link between potable and non-potable water, such as a hose. Backflow occurs when there is a high movement of water through a water main, which generates negative pressure in the cross connection, causing back-siphonage or backflow from the non-potable water source through the cross-connection, whether that be a hose or a pipe. This is due to
Bernoulli's principle.
Examples of cross connections can be someone dropping a hose connected to a sink into a mop bucket containing floor cleaner, or someone dropping an outside hose into a non-chlorinated swimming pool (green) or into puddle of water. Hoses, however, are not the only issue. An often overlooked connection is the direct water feed into chemical mixing systems. Hazards related to backflow are not always biological. Chemicals can be pulled into the water source, especially through this direct water feed into chemical mixing / dispensing systems.
Of course it is best not to make that cross connection, but this is not always easy when using hoses. Where hoses are used, it is important to make sure back flow prevention devices are installed.
Pressure deficiencies, such as when there is a water main break, also can result in backflow into the potable water source.
