I’ve been concerned about that in my house. It was built in 1955, and they used a lot of galvanized steel pipes. Eventually somebody did some additions and upgrades in the basement - adding a bathroom, moving the laundry, and something else I feel like I’m forgetting. The newer pipes were all done using copper and the fittings connecting the two are a third metal yet, I think they’re brass. I’m worried that I’ll need to replace all of the galvanized steel, which could be an issue since the pipes coming into the house are something I can, or maybe even should, change out until after the main shutoff valve. Regardless, I have some consultations to get someday down the road.