I use rainwater in my house for my water supply. I collect the water in plastic lined tanks. Some of my piping at home is copper, and I have blue stains in my shower, because I think the copper from my pipes is being dissolved by the carbonic acid in the rainwater. I'm planning to hang magnesium rods into my rainwater tanks, in the hope that these rods will react with the carbonic acid instead of my copper pipes. Does that make sense?