The answer to 'what causes repiping' is that there are several common reasons why a homeowner may need to repipe their plumbing system. The most frequent causes are old, corroded pipes that are leaking or have low water pressure, pipes made of materials that are no longer up to code (like lead or galvanized steel), or extensive damage from a plumbing emergency like a major leak or burst pipe.
Repiping involves completely replacing all the water supply pipes in a home, usually with more modern and durable materials like copper, PEX, or CPVC. This is a significant home improvement project that requires the expertise of a licensed plumber, but it can significantly improve the reliability, efficiency, and safety of a home's plumbing.