FAQ / Blue staining

Blue staining

Blue staining is where a noticeable blue/green discoloration is seen in bathroom sinks and similar
fixtures, commonly around plugholes and areas where taps drip or leak and occurs primarily in older
homes with copper plumbing (which may include copper underground pipe connections between
the water main and the house).

If your water is blue, run your tap until the water is clear.

Health NZ have advised that copper from household pipes is very unlikely to be a health concern,
especially when you run your taps until the water is clear.

If your water is blue, flush the water from your pipes until it runs clear.


Blue staining is caused by ‘cuprosolvency’. This is when water sitting in copper plumbing for a while
(such as overnight) reacts with the interior surface of the pipe and minute traces of copper dissolve
into it. If cuprosolvent water then comes into contact with a white bathroom sink, (for example),
over time the copper may leach into the sink itself, and staining can begin to occur.


There are two key actions to take:

1. Check taps and fittings for drips and slow leaks and get those fixed. Staining is most likely to
occur around plugholes where dripping water accumulates overnight, and down the back of
sinks/surfaces, where slow leaks run down from the taps. This is because the water has time
to sit and interact with the bathroom surface, and can evaporate, leaving copper behind.

2. Flush your taps and pipes by running them for at least 500ml when you turn them on,
especially first thing in the morning.

Cleaning blue staining

To clean blue staining, your best option is to speak with your plumber to get advice on the best products and methods for
cleaning blue staining, depending on what your fixtures are made from.

What can Wellington Water do about this issue?

Our drinking water treatment processes include adjustments to the water's chemistry to minimise
its natural corrosiveness as much as possible. Unfortunately, we can't eliminate the issue, as it's caused by
chemical reactions happening within the domestic plumbing of individual properties, which are
made up of different materials, of various ages and conditions.