In So.Cal.,what is the code # that tells what type pipe is to be used for in-house plumbing for propane?

The home now has PVC sch40 white water pipe installed for propane use. I just had a water heater installed and they used PVC to connect to the existing PVC for cold, and propane. Copper for hot. Installer said it is ok to hook up to PVC, using PVC if PVC is already existing. My propane guy won't hook up the tank to the system. He says PVC isn't to code, and isn't safe. Says it will leak through the walls of the pipe and fill the house with gas. Contractor says it's ok . Inspector says not ok. I can't find the section that describes what to use and what not to use. Help