sorry you did not get the copper piping you thought you would get but there are other types of piping that would be considered acceptable by plumbing inspectors. There is CPVC which is a plastic pipe with solvent weld (glued) fittings and there is PEX which is a plastic pipe with crimp fittings which are installed with a special specific tool. there is also threaded brass pipe or threaded galvinized pipe, but it is not likely that either of those two were used as it is much more difficult (and more costly) for your aplication.