Cross-linked polyethylene, or PEX, water tubing has been allowed in some locations for 20 years and pointedly disallowed in most others, but with the recent volatility in the copper price, resistance has begun to melt away.
Advantage: PEX has a lot going for it. It's easy to install using crimp and barbed fittings. Water flows through PEX silently, which is a big plus. PEX can take a freeze, and it's impervious to acidic soils, which destroy copper pipes. It will never rust or corrode, and internal turbulence is less likely to erode tubing walls. And finally, soft water won't leave traces of copper in your drinking glass.
On the downside, PEX installations often require more tubing and hangers than copper, and some manifold installations can waste hot water because you'll have to wait for it at each fixture instead of fixture group. You'll also need to buy one or more crimping tools, which run around $100. And finally, installations look messy, which bothers old plumbers a lot and young plumbers not at all. Put another way, PEX is the future.
Requirements: Some codes allow water-supply installations made entirely of PEX, while others require copper in the initial stages of the system-for its rigidity-usually at connections at the water meter and the water heater. Manufacturers make all sorts of copper-to-PEX conversion fittings, for both ends of a line. Another place for rigidity is at the fixture stub-outs.
As most household electrical systems are grounded, at least in part, through the home's metal water piping, an alternative ground needs to be established when converting to non-conducting plastics. PEX tubing comes in 20-foot sticks and 100- and 300- foot coils.
PEX is made in a variety of colors. plus clear, but most companies are gravitating toward red and blue, to signify hot and cold water.