SD,
Anti-Siphon is most common for household irrigation and I would say in the more frigid area that experieince freezing, the system needs be blown out with compressed are or "winterized. Larger commercial irrigation is different and utilizes Back Flow Preventers with in-line check valves. These BFP are also usually above ground so they can be checked/certified once a year. It probably is what ever your municipalities require to protect their main water pipelines from backflow contamination. In the States I have seen double check valve systems for fire fighting lines and also check for leaking in mainly static lines. JMHO

interesting. Lehua, thanks for that. around here, we use the large backflow preventers for larger multi housing complexes or commercial irrigation, but it is typically located either inside, in the "mechanical" room, or set below ground in an irrigation box. the duel checks for smaller residential we use these:

...Perhaps the reason I don't see anti-siphon valves around here maybe just local preference to having "invisible" irrigation? It's considered unprofessional to have a lot of above-surface parts. valves, filters, ball valves, blow out ports, even hose bibs are usually put below grade in an irrigation box.

Still curious if anyone has a theory why anti-siphon valves don't exist in interior BC, and also, wondering if that leaking around the "anti-siphon part" is normal?