If you live in or are buying an older home (50 yrs +) you need to be on the lookout for galvanized plumbing. This pipe was widely used in early 20th century buildings, up through the 1960s. Galvanized pipe was developed as a non-rusting option; a thin coat of zinc is applied to steel pipes to keep corrosive materials from getting to the steel. Unfortunately, it turned out that the pipe does rust—from the inside out and at the joints, causing clogging and leaks. While the rust itself does not necessarily cause problems with your drinking water, it can affect the taste and slow down the amount of time it takes to fill a sink or take a shower. Failures in the plumbing tend to be on a large scale, especially if older leaks have not been properly repaired. Some plumbers maintain that especially with older pipes, repairing one area can cause others to spring up. Galvanized pipes do have a fairly long life—40 to 50 years—and have been reported to last even longer in parts of the country where there is not a lot of corrosive material in the water. Areas where the pipe has been improperly joined with copper or brass can actually accelerate the corrosion.
Many owners of older homes report no issues with galvanized plumbing. However, if your home was built earlier than 1940, you may have a problem obtaining home insurance if there is any presence of galvanized plumbing, whether it is in good shape or not. (There are some homes built in the 1970s and 80s that used an inferior galvanized plumbing; most inspectors recommend immediate replacement.)
If you are worried about an older home, have a licensed plumber come in to inspect the situation before buying. If you already own and suspect you have galvanized plumbing, you can do a little of this yourself before calling in an expert.  If you scratch the pipe where it enters your home and it is a dull silver-gray, it's probably galvanized steel (copper will look like a penny, plastic is black). Look around and see if there are any rust spots, particularly at the joints. If you see rust, your plumbing may be at the end of its life. Do you find that it takes forever for your hot water to reach the shower? That could be a sign your pipes are clogged with rust. Your plumber can determine whether or not it is necessary to replace your entire system, or just certain pipes. You will probably not want to continue using galvanized pipe; it's expensive and much harder to work with due to the threading. Your plumber can help you choose a material that is right for you.
All pipes fail eventually. The secret is to stay aware of the condition of your home's plumbing and plan accordingly. If you know you have galvanized pipe that is beyond its life expectancy, the safest thing to do is budget for the eventual full replacement. If you are buying and small problems are already evident, you may wish to go ahead and do the replacement before moving in. Or, if you are already in the home, you might plan for yearly replacements in different sections of your home to keep costs and annoyance down to a minimum.
Many owners of older homes report no issues with galvanized plumbing. However, if your home was built earlier than 1940, you may have a problem obtaining home insurance if there is any presence of galvanized plumbing, whether it is in good shape or not. (There are some homes built in the 1970s and 80s that used an inferior galvanized plumbing; most inspectors recommend immediate replacement.)
If you are worried about an older home, have a licensed plumber come in to inspect the situation before buying. If you already own and suspect you have galvanized plumbing, you can do a little of this yourself before calling in an expert.  If you scratch the pipe where it enters your home and it is a dull silver-gray, it's probably galvanized steel (copper will look like a penny, plastic is black). Look around and see if there are any rust spots, particularly at the joints. If you see rust, your plumbing may be at the end of its life. Do you find that it takes forever for your hot water to reach the shower? That could be a sign your pipes are clogged with rust. Your plumber can determine whether or not it is necessary to replace your entire system, or just certain pipes. You will probably not want to continue using galvanized pipe; it's expensive and much harder to work with due to the threading. Your plumber can help you choose a material that is right for you.
All pipes fail eventually. The secret is to stay aware of the condition of your home's plumbing and plan accordingly. If you know you have galvanized pipe that is beyond its life expectancy, the safest thing to do is budget for the eventual full replacement. If you are buying and small problems are already evident, you may wish to go ahead and do the replacement before moving in. Or, if you are already in the home, you might plan for yearly replacements in different sections of your home to keep costs and annoyance down to a minimum.