Galvanized plumbing supply pipes are made of steel and coated with zinc. They are not a good choice for supply or waste pipes on a plumbing system. These pipes were common in older homes but have not been commonly used since the 1960s. If you have a home with galvanized water pipes they may leak and need replacement at any time. Decay and corrosion on these pipes is not usually observable as it happens on the inside of the pipe - the outside remains pristine. Galvanized pipe decays by rusting and having scale / hard water deposits inside. A sign of failure is reduced water flow. If your house is on public ("city") water supply the estimated life span of these pipes is around 50 years. Deterioration happens faster when the home is supplied by well water, which is almost always moderately to very hard. When you see a decrease in flow or rust on the outside of this material it should be replaced.