I have read NFPA 25-11 18.104.22.168, and when it states the "sole water supply is through a backflow preventer and/or pressure reducing valves" require quarterly testing. What exactly is "sole water supply"? Is this the main water supply to the building, or some cases suppression systems are fed off of a municipal water line. I know this is too simple, but want to make sure my assumptions are correct. thanks.