Where is PEX approved for use?
PEX is an approved material in all the current edition national model-plumbing codes; however, some jurisdictions using older versions of these codes may not have amended the code to include PEX tubing . Contact the local authority with jurisdiction over plumbing to verify the acceptance of PEX tubing for plumbing applications in your area.
Question and answer courtesy of Plastic Pipe and Fittings Association (PPFA). More information is available at: http://www.ppfahome.org/pex/faqpex.html