In regard to what? The safe water Drinking act or the NSF or the Local or state or federal codes? How about the AWWA standards OR the ASSE Are we talkig back flow from Boiler feed water? if so see ASME sect IV
Sylvan is right. In regard to what? The safe water act makes the water supplier responsible to the last tap on the system. Different jurisdictions have different programs. For example, in Anne Arundel County Maryland, the water company handles the backflow situation. In Tucson Az, the water company makes the individual user pay for the backflow install and yearly certification. Are you talking about Reduced Pressure principal?