Backflow is the unwanted reverse flow of contaminated water through clean water in cross connection systems. A cross connection system is one that has any connection between a public water system or consumer’s potable water system. For example, domestic water, fire, irrigation, boiler, and chilled water systems that connect with either public or consumer water systems are considered cross connection systems.
In order to prevent this contamination, backflow prevention devices are set up. The device commonly consists of a pair of mechanical valves, that hinders dirty water from reverse flowing in an unexpected change in water pressure. These devices must be checked to ensure they’re doing their job, which is where backflow testing comes in.