A lot has to do with what thr ewater ph is in regards to copper or other metals being able to leech out of the pipes and into the system. Normally hotter water is goning to leech metals faster, but no one uses hot water for an aquarium. There is no telling what metals you r water may be in contact with, but for the most part if your ph is in a reasonable range copper and any other metal is not going to leech out and cause a problem. The old wives tale of copper in a aquarium etc being deadly, yes, its true, but odds are the ph that is needed to create a copper problem is gonna kill the critters long before the copper itself does.