A back-flow preventer keeps contaminated water from re-entering your household water system, and should always be used when applying fertilizer. A back-flow preventer, when used, is the first item in your line after your faucet or hose bib (hose thread). If used with a battery operated controller, install the back-flow preventer after the controller to prevent stress on the back-flow device. For faucet installation only. Do not install on main line.
