Old Galvanised Pipes


Galvanised pipes are zinc coated steel pipes. The zinc is a sacrificial layer that blocks the iron in the pipes from oxidising (i.e. rusting). Many older homes in New Zealand still have galvanised pipework in their plumbing systems.


If you have an older home there could be galvanised (“galv”) pipes that you are unaware of hidden underground, under floors, in ceiling spaces, within walls or in plain view but painted. A simple test with a magnet will identify them (NB. The magnet will adhere to steel but not plastic or copper).

What’s the big deal with galv pipes ?

Simple put with age galvanise pipes fail. It can be a gradual deterioration that you may not notice. The internal lining goes first, and the pipes corrode from the inside outwards.  When you look at a pipe it may appear fine but inside it is likely to be a rusted mess. The rate of deterioration depends on a number of factors including but not limited to the quality of the pipe, water acidity and mineral content, and household wiring (i.e. earthing through pipes that can hasten electrolysis).

Signs of trouble

There are some tell-tales of a failing galv pipe:

  1. Flow

The water flow may become restricted as layers of rust build inside the pipe.

This can be noticed if you have two similar taps on the same piping branch at the same height but one flows more strongly than the other. The situation should be investigated as there will be something wrong either with the tap or the intervening pipe (or both). 

It is more difficult to notice flow restriction if the fault is before the house (i.e. a galvanised water main). All taps will appear to be performing similarly. A deterioration in water flow may incorrectly be attributed reduce council water pressure.  

2. Discolouring & Tainting

Porcelain toilet pans and basins sinks can become discoloured. Orange rust stains are a sure sign of trouble. You may also notice that drinking water tastes of iron. 

3. Grit

As the pipe rusts it forms layers that can de-laminate or shed particles into the water supply. The particles can clog filters and jam taps and appliances. This is when it starts to get expensive – taps and appliances will need to be replaced. Yet, these new replacements will be subject to the same conditions and will in turn also fail. 

4. Exterior rust marks

The rust will eventually  worked it’s way through the steel pipe and will become visible on the outer pipework. The spots will swell and, if painted, the paint will flake. It is too late to try rust prevention techniques – a rust killer will not fix the problem. 

5. Leaks

Trouble is nigh. Pin-hole leaks will develop into drips. As rusting accelerates the weakened pipe will rupture. (Note: If this is happening now isolate the house and call Seal Plumbing & Gas Services.)



Rather than exposing your home to this chain of events get the pipework sorted. Seal plumbing and gas services can check your property. Proverbially, “a stitch in time” is a better plan than “burying one’s head in the sand”. Don’t minimise the problem or risk, for when it comes to galv pipe, the situation is probably worse than it looks and it wont get better by itself. If you think you may have galvanised pipework call us. We can make a plan with you to switch out the old galvanised pipe for copper or butylene alternatives.