I am in the swimming pool business and we run into something similar. I've only seen it myself on jobs with salt water chlorination or really crappy tap water with lots of metals in it. We use sacrificial anodes to fight it. The ones we use have a bonding lug built in and you are supposed tie that in with the existing pool bonding wire (all pool shells, ladders, rails, and equipment that's metal are connected with a bonding wire)