Copper piping and cathodic protection?

[Ken Fabian]

We rely on collected rainwater for household water. We get some copper staining via the cold water taps but not the hot water. The hot water system has a sacrificial (cathodic?) inclusion - I think it is zinc.

I was thinking of adding a piece of zinc into the rainwater tank to stop what is slow corrosion of the copper pipework - and prevent that staining. Changing pH by periodically adding chemicals does not appeal - and would require regular water testing and treatment. Anyone here that could advise on whether a piece of zinc (perhaps hanging inside the water tank) would work? Or offer suggestions?