For drinking water:

• An evaporator plant won't care tuppence, as it will operate quite happily with any old rubbish that is thrown at it, provided it is well-maintained and operated.
• For a reverse osmosis plant, the chlorine levels should not exceed 0ppm, otherwise irreversible damage to the membranes will occur, and quite quickly. Chlorine is often knocked out by dosing sodium metabisulphite [SMBS] in slight excess, and invoking the plant's start-up and shut-down sequences using ORP measurement on the water downstream of the SMBS injection point.