I don't know for sure but copper pipes might hurt the live rock, but I don't know because I used PVC on my tank. Did you but the R/O from a fish store? If you did call them and see if they know if it will hurt the LR. I used to have a FOWLR tank but now I'm all reef. I know it will hurt some if not all reefs, I did use copper pipes on my R/O for my reef and it killed several corals.
Using a product like Prime will help neutralize the effect of any copper that leeches from your home plumbing. Treated tap water is considered ok for FOWLR tanks. Treat it first, wait about half an hour then use it as make up water or add salt to make water changes with.
Personally I prefer RO/DI as it is a known source without any added pollutants. Over time any "extras" that come in with your tapwater could lead to algae problems. However this can be easily circumvented by the types of fish you buy.
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