"Any plumbing from the '60s or older is on its last legs," says Howard Maxfield, a long-time home inspector in the greater Seattle area.
Anytime copper piping has been attached to galvanized pipes, dielectric coupling is required to stop the corrosion caused by dissimilar metals touching.
Unfortunately, these junctions may be hidden inside the walls.
If a plumber did the replumbing, it certainly should be correct. On the supply side, all piping on the house side of the meter belongs to the homeowner, and everything on the street side belongs to the water district.
For a quick test of an old house, turn on the hot water.
If the pressure is low, the house probably has galvanized pipes that have corroded and plugged up. The house could have good pressure in the hot-water lines, but still have unseen galvanized-pipe problems.
It is possible that only the bad pipes were replaced, leaving lots of old galvanized pipes still in the house and either in need or soon-to-be-in need of replacement.
Experts will tell you to replace the entire piping system when galvanized piping starts to go bad, but that is pricey, and often homeowners opt for the more economical, halfway fix by repairing only the pipe that is the immediate problem.
Worse, the bad galvanized pipe may have been replaced with more galvanized pipe instead of copper or plastic pipe, meaning the problem has just been extended, rather than cured.
It's difficult to determine the entire plumbing picture, since most of the system is behind walls.
Maxfield says to look under the sinks to get some understanding -- often, plumbers run new pipes up through the floor under the sink instead of through the wall, he says, so you can see where there is new plumbing.
If the house has a crawl space and you're not too discomfited by going into it, you can get a better picture of the plumbing status.