I use tap (*gasp*), it can be fine depending on your local supply; NO3 and PO4 are undetectable in our water.
Not all houses/buildings use copper pipe, some use steel and even plastic (though plastic is for cold water only). Our building is around thirty-five years old, so the pipes are far from new. The new bits they've installed in our unit are all steel. Old pipes have a buildup inside, whereas new copper pipes without a buildup probably transmit a lot more Cu into the water.
I'm no plumber and could be incorrect, I just see new copper pipe near a reef as a disaster waiting to happen. If the water is going from the copper pipe into the RO unit I wouldn't worry, but if it's for transmitting water to the tank I'd refit with steel or plastic. You can run Cuprasorb from SeaChem if you think there's copper in the water already.