Final answer:
The specific time required for running a Reverse Osmosis system prior to chlorine testing is not provided in the reference and varies by manufacturer guidelines; thus, the user should check the manual or professional recommendations.
Step-by-step explanation:
The question on how long does the Reverse Osmosis (RO) system need to be running prior to chlorine testing does not relate to the provided reference information concerning urine output after drinking water. Therefore I am unable to provide a specific time based on the given reference.
Generally for a new RO system, it is recommended to run the system for a period to flush the system and stabilize the membranes which may vary according to the manufacturer's recommendations. It is important to consult the specific RO system's manual or professional guidelines to determine the correct flush time before conducting any chlorine testing.