Backflow testing is all about Safe Drinking Water as regulated by the safe drinking water act [SDWA] of 1974 and amendments. 

Backflow protection is required an all potable water cross connections according to the level of Hazard potential.

The Backflow Assembly shown is on a Lawn sprinkler system connected to a potable water supply.

Testing and maintaining properly installed Assemblies is the only way to know if it is working properly.