In order to insure the proper operation of a backlfow assembly, it must be tested and certified upon installation and periodically thereafter as required by state code. If the hazard (substance you are protecting against) is considered a high hazard (i.e., a hazard that can cause health problems), the State requires that the device be tested twice a year.
If the hazard is considered a low hazard (such as the hazard effects only the taste and odor of the water), the State requires testing once a year.