Exposed to moisture and prone to accidental shovel blows, buried water lines must be made of materials that resist both deterioration and punctures. Longevity is particularly important for inaccessible pipes, such as under-slab supply lines. Plumbers use several types of pipes to construct underground service and water lines, including synthetic and metal pipes. Because climate and site conditions often affect a pipe's performance, it's best to consult local codes or a building professional before installing an underground water supply line.
Familiar to novice gardeners and landscapers, polyvinyl chloride (PVC) pipes securely deliver water both above and below ground. Although PVC is available in a wide variety of types, standard home improvement stores commonly stock a white, thin-walled schedule 40 PVC and a gray, thick-walled schedule 80 PVC. PVC pipes connect via a gluing process -- called solvent welding -- or with threaded, screw-like fittings. Although some municipalities allow PVC for residential potable water transport, many areas restrict PVC to irrigation water delivery systems.
Like PVC, chlorinated polyvinyl chloride (CPVC) is a plastic pipe that carries water supply both above and below grade. However, CPVC withstands greater temperatures and pressures than standard PVC. Therefore, manufacturers rate CPVC suitable for use in both hot and cold water systems. Like PVC, approval of CPVC for interior potable water supply varies according to local codes. Among its above ground applications, CPVC is frequently utilized in recreational vehicles and manufactured homes.
Plumbers often use copper to connect underground water service lines. Although copper pipes are rigid and resistant to corrosion, copper pipes deteriorate under certain soil conditions. Where soil or site conditions threaten to corrode copper supply lines, builders often sheathe the copper pipe within synthetic sleeves. Unlike other materials, copper has near universal code approval for a broad range of applications. However, the cost of copper fluctuates with changes in the metals market and copper pipe is generally more expensive than plastics such as PVC and CPVC.
Cross-linked polyethylene, or PEX, is a plastic water supply line suitable for both buried and above ground applications. Like a thick, strong hose, PEX is a flexible tubing material capable of stretching around bends and turns without pipe fittings. PEX withstands chemical damage, high temperature and high pressure. Unlike PVC and CPVC, which connect via glued fittings, PEX connects via threaded, compression fittings. PEX is utilized underground for potable water applications and embedded within concrete slabs for radiant flooring. PEX's code approval varies by community.