To answer your questions:
* This is a battery manufacturing plant. My focus is on quality control of incoming and process acid, but the RO water is what is used to dilute the concentrated acid. We have an outside vendor that monitors and services the RO system.
* The feed water/raw water is city water. No chemicals added to feed or RO water.
* Within the scope of my testing, I haven't seen any changes to the feed water. I don't have a full array of tools to test water, so for water I can do elemental analysis by ICP-OES, Cl- and NO3- by UV-Vis, TOC by titration, and pH/conductivity by laboratory benchtop meter. For anything else, we have a good outside lab that also handles the water testing for the municipal area we are in. My next move may be to send them samples for whatever water tests they recommend.
I have a smaller, independent RO water system in my laboratory (using the same city water as feed) that in turn feeds my DI water system. The pH of that RO water is consistently 6.7-6.8.
Water treatment is not my specialty, but my understanding from the literature I have read is that RO water, being fairly pure water, typically has a pH that is near/somewhat below 7. CO2 easily dissolves in this water, creating carbonic acid and thus driving the pH below 7.