I was right up front that this clown should not be screwing around at a restaurant, of all places. If Tom wants to knock him on his duff, I'll be happy to hold him. Just so that's crystal clear.
Yeah, really. People don't eat at heavy industrial and sewage treatment plants.
I could take the opportunity to improve my knowledge by asking about double check valves, and what's the change of air break distance, and why is any distance beyond "above the max flood level" meaningful, and what are the likely screwup points in a restaurant that might or might not occur in a home... but I think I'd rather stay on the education topic generally.
It shouldn't take a 4 years as an apprentice plus four years as a journeyman to work on my own stuff. On the flip side, I'm sure it should take that long before I ought to be working on the kitchen of a high rise hotel. Not everyone interested in acquiring a skill wants to do it for a living, but everyone acquiring any skill wants to use it to their own benefit, directly or indirectly.
If it's a matter of taking a course or three, passing practical and written tests at the end, and then I get a limited license good only for getting permits on premises I reside in, sign me right the hell up please.
That said, it's not the licensing requirements that prevent water-contaminating incidents, it's the inspection process proving that code requirements have been complied with independently of the profit motive. I can appreciate their workload only allows limited time showing homeowners what they did wrong, and I'm all for schemes to dissuade the true morons. Simply locking out not-for-a-living folks is unreasonable.