Over decades, my house has accrued a mix of galvanized, copper, and pex pipe. I've been told that one "should stick to one type of metal in your pipes or use pex." (here)
As long as dielectric unions are used where they meet, is there a problem with having both galvanized and copper in the same system?
If there is a problem with using both metals, what is the correct use case for dielectric unions?