What are the main reasons for locating the master valve at the discharge of an RPZ backflow preventer instead of the inlet? My best guess is that the water pressure to the RPZ will be more consistent and so the RPZ's valves' seats won't experience as much wear and tear. I cannot think of how there is a greater risk of cross connection contamination with the master valve at the inlet to the RPZ, but maybe I am missing something. My HOA's board is asking. A few of its 70+ RPZs have the master valve at the inlet to the RPZ. The city has suggested, but not mandated, ensuring all the master valves are at the discharge of the RPZs. The HOA's irrigation system is some 25-years-old and has been modified many times over the years. It originally had AVBs. Thanks in advance for your pro bono help to my blue collar neighborhood.