Galvanized(potable water)

Before copper tubing became the pipe of choice for water distribution inside of homes, galvanized pipe was widely used. It's installation requires threading the ends of the pipe and screwing the pipe and fitting together using a thread sealant(pipe dope).

Galvanized pipe can still be purchased and used. It does have a variety of applications, but standard water distribution is no longer one of them. Besides being difficult to work with, it has the same problem as galvanized drain lines. It rusts, from the inside out.

There really isn't any way to determine how badly corroded a galvanized pipe is. Leaks aren't too terribly frequent, but the problem becomes very serious when the pipe needs to be worked with. The thinest part of the pipe is where it was threaded, and generally a weak pipe will break near that point. This leaves a small portion of pipe left in the fitting, often leaving the fitting unworkable.

Galvanized water pipe is considered five star work because of the serious potential for disaster. Often, when a piece is attempted to be unscrewed, it breaks. This requires you to go back to the next available fitting, which may also break, and perhaps the next, and the next, leading to considerably more pipe to be replaced than expected. There are times that this could lead into places that may not be accessible, which can seriously complicate matters.

A female fitting can generally be considered safe to start from. A backup plan, however, should always be in mind. If the fitting comes loose, great! If it breaks, it could lead to problems you're not prepared to deal with.