In drinking water systems installed inside buildings, polyethylene (linear or cross-linked PEX) are used. The advantages of PEX include its long life, its corrosion resistance, low cost and easy installation. PEX is currently the most commonly installed plumbing products in new residential buildings, ahead of copper and CPVC (chlorinated polyvinyl chloride) polychlorinated polyvinyl chloride. Due to hygiene requirements, particular care must be taken to avoid leaching from pipes substances escaping from pipes.