My house has the original galvanized steel pipes, and last year many neighboring homes were repiped because the original plumbing was in bad shape. I inspected some of the pipes in my house and found they were almost completely plugged by deposits. Plumbers in this area recommend replacing the steel pipe with copper and say it will outlast steel pipe, yet they guarantee their work for only five years. Both will do the job well. It's a matter of economics.
Copper is the dominant material for tubing and pipe in the residential plumbing market.
Galvanized pipe is rarely used. According to the Copper Development Association, copper tubing is used in about 90 percent of residential potable-water systems, with the remainder of the market divided between galvanized steel pipe and plastic pipe and tubing. The labor costs are greater to repipe with galvanized compared to copper. It takes longer to thread steel-pipe joints than to solder copper pipe. Also, a plumber can bend copper tubing for a slight change in direction.