Galvanised pipes became a popular fixture in American homes when it was thought that they would resist rusting better than other types of pipes. As it turns out, galvanised pipes are prone to rusting from the inside of the pipe, which can constrict the flow of your water, and potentially contaminate the supply.
Check to see whether there is a rust problem in the galvanised pipes. It will be clear if you have a build up of rust in the pipes as the flow will be badly constricted and the water supply may be reduced to a trickle.
Purchase a chemical pipe cleaner. A product such as this should have the required power and effectiveness to wash away the rust when you apply it. Chemical cleaners are readily available at most hardware stores.
Apply the pipe cleaner to the pipe. Instructions may vary depending on which brand of pipe cleaner you have bought, so follow the instructions on the bottle and apply the pipe cleaner. Leave the cleaner to circulate for as long as instructed on the bottle.
Rinse the pipe with water. When the pipe cleaner has circulated in the rusted pipes, run the taps and let the water rinse the pipes. After a small amount of time the water supply in your home should be less constricted.
When the galvanised pipes begin to rust it really is the beginning of the end. A chemical pipe cleaner is the only way to wash out the rust, but it can also wear away at the weakened pipe. You should be prepared to replace the pipe not long after the rust appears.