PEX underground water lines are a special type of water line homeowners can use that have several advantages over rigid pipes, such as extreme temperature tolerance and the ability to flex and bend to get to difficult-to-reach areas of the house. "PEX" is shorthand for cross-linked polyethylene, the material from which the piping is made.
PEX water lines can withstand temperatures from below freezing up to 200 degrees Fahrenheit, making it useful for things such as radiant hydronic heating, snow melting applications and hot- and cold-water plumbing options. PEX piping also has fewer fittings, which enables the choice of various types of design options, such as tree and branch, manifold and remote manifold systems.
Additionally, PEX piping is quieter than normal rigid piping, and its unique interior is smooth, which resists scale buildup and corrosion, two factors that can affect water flow over time. PEX is also freeze-break resistant, and the price for installing it compares favorably when compared to rigid water piping.
However, the piping system is not without its drawbacks. For one, it is only freeze-break resistant, and not freeze-proof. It is also not advised for above-ground use, as UV light reacts negatively with polyethylene. PEX also caries with it some chemical exposure concerns and is not recommended for underground water supplies, even if reduces the amount of UV light that affects the pipe.