According to the PPFA, PEX is manufactured and tested according to four national consensus standards: ASTM F876, Standard Specification for Crosslinked Polyethylene (PEX) Tubing; ATSM F877, Standard Specification for Crosslinked Polyethylene (PEX) Hot- and Cold-Water Distribution Systems; AWWA C904, Cross-Linked Polyethylene (PEX) Pressure Pipe, 1/2 In. (12 mm) through 3 In. (76 mm), for Water Service; and CSA B137.5, Cross-Linked Polyethylene (PEX) Tubing Systems for Pressure Applications. ASTM International is an international standards organization that predates other standards organizations, the American Water Works Association (AWWA) is an international nonprofit association founded to improve water quality and supply, and the CSA Group is a Canadian standards organization comprised of representatives from industry, government, and consumer groups.