A backflow device is a valve that is installed on a water line that only allows water to flow in only one direction. It is a device that protects the safety of a public water supply. If there is any kind of contamination to a water supply, and by a back syphon, that contaminated water is drawn back into the public supply, it could be hazardous for anyone along that line using that water. A backflow device has a check valve in it that will slam shut if water begins to “back flow” in the opposite direction of what it should be.
By any town code, all commercial locations should have a backflow device installed, whether it is a double check valve, or an RPZ valve, the local water authority would be the proper agency to spec out which device is required for your establishment.
A double check valve is required for residential applications where there is an underground irrigation system installed. The reasoning is, since we use fertilizers and pesticides on our lawns, if there is a break in an underground line, and a back syphon draws water that is contaminated with fertilizer back into the public water supply, this will affect all user along that supply.
Backflow devices can only be installed by certified plumbers. In Suffolk County, you must hold a Master Plumber’s license, and be state certified to install and perform the required annual inspections on any backflow device.