Yall got me curious so I looked up a couple of RO systems on the internet. I think you're both right, sort of. The systems I looked at had sediment/carbon pre-filters (1 or 2). Carbon to remove chlorine to protect membrane. Then a final "polishing" carbon filter after the RO to improve taste even more. Now I'm no expert, so could be wrong.
I'm no chemist either, but I used to sell water distillers way back when. RO systems were my primary competition, so I got pretty smart about them. I was pretty sure of the fragility and need to frequently replace membranes. This is not a ploy by the companies to sell razor blades. They really do overload with stuff, and eventually either clog or break down. In extreme cases, they actually tear. One of the derivitive problems is that the user typically has no way of knowing when this happens. To be safe, the manufacturer recommends a PM schedule that includes changing the membrane periodically.
Regarding the specific issue of chlorine, I went to the same place y'all are getting your info from, too (the good 'ol net). I went to the Culligan web site and looked at the commercial Culligan RO unit specs. They list the tolerances of things in the water as it enters the RO filter. Max Chlorine is listed at 0 mg/L. Not really knowing what was meant by this, I checked a few other sources, and sure enough, not a one has a warranty that covers the damage due to chlorine, so they always have that upstream filter in the residential/low pressure systems. Bottom line, it is unlikely that any chlorine gets to the holding tank, since the 5 micron filters in use on these systems is designed to specifically filter out chlorine, among other things, and will clog before a chlorine molecule (or ion) passes thru it.
<font color="blue"> Bottom line, it is unlikely that any chlorine gets to the holding tank </font color>
This is consistent with what I know, which is simply based on my own RO system. All of the filters are in line before the membrane. The water that goes into the tank is not filtered again after the membrane, so that would mean that there is no chlorine in the tank.
This makes sense, as pure water in an enclosed environment isn't a good growth medium for bacteria - the buggies need some kind of food to live on. Furthermore, the small RO tank is emptied and refilled often enough that bacteria growth shouldn't be an issue in any case.
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