In researching RPZs, I found the following web site (link below.) It is by a group of people evidently trying to fight backflow preventer requirement in their area.
I cant believe these people would seriously make these claims (for example they claim RPZ and other backflow devices are against Homeland Security Laws because they make it easy for terrorists to inject toxins into our water supply, so if you put one on your house you are aiding terrorists) but I guess they thought/think it will persuade lawmakers. Anyway, I found it amusing and wanted to share:
http://www.suncitydave.info/reasons/