Reply #5: This is a big concern for old systems, not for new ones

[jmowreader]

New systems, and new additions to old ones, are all done in either Schedule 60 PVC or in crosslinked polyethylene (PEX) pipe, because plastic pipe is less expensive to purchase, less expensive to transport, easier and faster to install, the tools are cheaper, and it's easier to find plumbers who work plastic than work metal today. Plastic pipe doesn't corrode either. In areas where the ground freezes routinely, they use PEX because it's flexible. There are transition fittings available to let you couple plastic to metal.

No one sits around planners' offices wondering what metal pipe technology is best for the job at hand; they install plastic pipe and are done with it.

There are places where you must use metal pipe. All gas service is metal pipe, including compressed air. Steam service is metal. Sanitary piping (foods, drugs, that kind of thing) uses metal pipe (specifically, ASTM 304 stainless steel) because they clean it with steam. Chemicals are handled in metal pipe, as are petroleum products. Most people plumb the hot-water side of water heaters with copper. Everything else went to plastic long ago--and some guys are starting to transition water heaters into CPVC with copper or stainless flex lines.