Combining Lead pipe with Zinc or Copper pipes in a domestic water installation Grateful if someone assists in explaining this example that appears on a high school text book. The problem can be summarized as follows:
&quot;Old water networks supply water to a residential area via Pb lead pipes. A user wants to fit his own  installation with pipe made out of either Zn or Cu.  The intent is to reduce the lead presence in the water. Condition: the lead pipe of the municipality will remain unchanged up to the water gauge/meter at the house input.
Account for the presence of O2 in the water and give an explanation on your choice Zinc or Copper.&quot;
The solution suggested in the book shows Cu pipes, and excludes the use of Zn.
I would chose Zn. Reason would be that O2 would preferentially oxidize Zn instead of Pb. Thus preventing the formation of Pb oxide/hydroxides and consequent leaching in the water.
Thought I overlooked something and looking for an explanation to the book' choice which I assume is correct.. thanks for your support
The focus of the analysis should be first on the anodic index (see, for example, table here), which relates to the electrochemical corrosion potential of the metal serving as the anode. Second, materially important is the current state of the old municipality Lead pipes.
Per the source, the anodic index of Pb is high (see chart) above copper, so historically it has already electrochemically corroded likely inducing a protective Lead oxide coating in the presence of dissolved oxygen.
However, Zn metal is more anodic than the Pb anode, and as such, would readily corrode and may introduce high levels of Zn ions (even levels considered problematic/toxic).
As such, copper metal, which is lower in the anodic index relative to the Pb electrode, is likely a better choice to preserve the current state of affairs, which is in apparent agreement with the reputed cited textbook 'correct' answer.