I am considering selling my home and while I was in my basement inspecting the water supply pipe, I noticed corrosion there. I have attached a picture of my concern. What is causing this and how can it be repaired? Also, I am not sure if it makes a difference, but I have well water.
Signed, Dave,
Pleasant Prairie, Wisconsin

Hi Dave, thank you for contacting me with your question. What you have going on is called galvanic action. Galvanic action is the process by which the materials in contact with each other oxidize or corrode. In most residential plumbing situations, the process is caused by galvanized plumbing pipes that are in contact with copper water supply lines. I usually explain to my home inspection clients that galvanic action is like the relationship between Democrats and Republicans. They do not particularly like each other’s views and they often argue. The good news is that the repair process is rather simple and is not that costly as long the water supply lines are accessible. Installing a dielectric union will eliminate the galvanic action. As far as well water, the minerals that can be in it accelerate the galvanic action and corrosion. If left in place, the water supply line will eventually corrode at the point of contact. This is something that I often come across when I inspect older homes, mostly in the county, where well water supply systems are more common. However, I recently inspected a home that was supplied with municipal water and discovered galvanic action at the water supply lines where a galvanized pipe was in direct contact with copper pipe.