For example, under some circumstances bacteria can grow better on plastic pipe surfaces than on copper pipe. While not all these bacteria are harmful, production of safe drinking water requires elimination and control of bacterial growth at every reasonable opportunity. Certain chemicals can also migrate into drinking water through plastic pipe. In addition, because plastic is non-conductive to heat and electricity, plastic pipes might be more prone to bursting in very cold weather and cannot be used to ground electrical appliances. This list is not meant to discourage use of plastic plumbing, which obviously has its own merits, but it is merely provided to show that there is no perfect plumbing material that could be economically used in all situations.
Tire wear on a car is a good analogy.
Normally, the tire tread will wear down uniformly over the years and the tire will last as expected. However, if a nail were to puncture the tire, in effect causing excessive tire wear at one point, even a new tire can fail long before it should. There are many ideas on this subject. The list includes factors arising from improper installation, bacteria, electrical grounding, pipe manufacture, water quality, or a combination of these and other factors. While some individuals may strongly believe that one or more of these factors is involved, to date scientists have been unable to identify a cause.