There are many potential causes for pipe and plumbing leaks, from negligence on the part of either your contractor or the homeowner to simple age, wear, or sudden force and catastrophe. The most common cause of a leak is just age and wear — PVC piping lasts for around two to three decades, and then begins to degrade. Other materials have a similar life span, with the exception of modern PEX, which is longer on average.
Your typical plumbing leak can be caused by:
Wear and tear due to age
Sudden trauma to pipes caused by water pressure or outside force
A buildup of corrosion, mineral deposits, or rust
Tree root intrusion
Frozen or burst pipes