If there's even a chance of copper in your tap water, I'd avoid using it at all costs.
Last week, I needed to do a top up on my 20 gallon reef tank. Normally I only use bottled RO water that I have delivered to my house every few weeks. With the sudden rise back up in tempatures outside, I wasn't prepared for extra 1 inch of evaporation.... So... I used tap water. I put in stress coat, de-chlorinator, de-chloramine -- I added it all!
Not even EIGHT hours later there was major crisis in my tank.... I've had to do a 25% water change evert day for the last 6 days. I lost a brittle star, a percula, 5 crabs, 8 snails and who knows what else there is that I can't see.
This has been the biggest aquarium disaster I've had yet (hopefully the last) and it all resulted in adding tap water that had copper in it.
BTW, my tank is still showing 0.05 copper.. which is amazing considering it was 0.29!