Final answer:
Plumbing systems that were legally installed can continue to be used, maintained, or repaired as long as they don't pose any hazards to what was created by the system.
Step-by-step explanation:
Plumbing systems, lawfully in existence at the time of the adoption of the building code, may continue to be used, maintained, or repaired as long as the original design does not pose any hazards to what was created by such plumbing system. This means that if a plumbing system was installed according to the code requirements in place at the time of installation, it can continue to be used as long as it is safe and does not create any hazards.