The most common pipe leaks are in galvanized water piping systems in older homes. Galvanization consists of an application to the pipe of a protected layer of metallic zinc by either hot-dip galvanizing or electroplating. Zinc is traditionally used because it is cheap and adheres well to steel. Typically, galvanized piping rusts from the inside out, building up layers of plaque on the inside of the piping, causing both water pressure problems and eventual pipe failure.
If not repaired or unnoticed, pipe leaks can cause mold that is dangerous for health and particularly destructive to property. Mold can grow behind walls, under floors, in ducts, in carpet pads, and behind ceiling tiles. By the time you discover it, the mold can have caused severe property damage.