This seems like a scam. Explain to me why a backflow preventer is so critical that it needs professional annual inspection ($35, which in 2min of work ends up being $1000/hr). How is my sprinkler system that is downhill of the water main supposed to backflow against 40 PSI of pressure? The water in the sprinkler system came from the water main, so at worst it just returns the same water that was already there.
There's about 5 assumptions here that aren't adding up to anything resembling a remotely possible threat.
- water can flow uphill
- non-pressurized water can force past a 40 PSI mains pressure
- A valve isn't enough to stop water flow
- safe water magically turns dangerous when it enters a sprinkler pipe
- the backflow preventer and water valve will fail, and annual inspection will remedy this