I'm not a chemist, but i can understand how an infinitesimal amount of copper ions can swim around in solution but gradually take on weight and clump together as they react and bond with other elements.
Or at any rate the copper can go from water soluble to insoluble as it picks up friends.
I readily admit that i have a sesame street perspective on that.
I know a chemistry professor (Well, a guy with four degrees who runs the magnet lab for the chemistry and biology departments of a university) who could provide the whole technical explanation, if i wanted to bother him with it.
Pretty sure the reason we use copper pipes is the same reason ancient romans used lead pipes: It's easy to work with.
