I don't know about you guys but when I installed my lawn sprinkler system I found out that code was to have double check and anti-siphon valves to protect against this very thing. I also found out there was no such code for our domestic water system so I installed double check and anti-siphon valves on my domestic water supply at the entrance to my house just after the meter.
(Brewmaster and Pitmaster)
BBQ Team: Lawn Guyland Smokers
Brewery: Black Dog Brewery
"Sam I Am": XL Big Green Egg
"R2 and D2": Twin 22" Weber Smokey Mountains
Custom Made Automated Souped Up Sabco