A backflow preventer is a device that’s installed on water pipes that allows water to flow in one direction but never in the opposite direction. Its sole job is to prevent potable drinking water from being contaminated due to backflow. The risks to drinking water quality from backflow contamination incidents pose a constant threat—whether they’re nuisance, non-health hazards, or serious public health events. Plumbing codes mandate that potable water supplies be protected against backflow at all cross-connections.