I think that varies by state. I know when I did construction work years ago, a person who actually tapped into potable water had to have at least a journeyman's license, and the inspectors would actually come out to check. A tag with the journeymans' license number had to be afixed to it when it was finished. There were other tasks with those requirements too. Now you rarely see the guys. The master plumber just passes out signed tags to his illegals. I know in the northeastern states they still poilice the crap out of that stuff to keep the illegals out.