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).

What causes blue staining?

It’s a sign of a phenomenon technically known as ‘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. 

How do I prevent blue staining?

There are two key actions to take – first, check taps and fittings for drips and slow leaks, and if possible, 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.

The other important piece of advice is to flush your taps and pipes by running them for at least 500ml when you turn them on, especially first thing in the morning.

This flushing is actually standard Ministry of Health advice, and applies to all homeowners, even when there are no signs of staining, and in properties without copper plumbing. It’s a simple precaution to manage the potential risk for small traces of any other heavy metals to have accumulated in the water overnight, when water is used for drinking, cooking or brushing teeth, which is known as plumbosolvency. More information on plumbosolvency is available here.

Why are you recommending we flush taps at the same time as there’s a total outdoor water ban?

Flushing 500ml of water first thing in the morning before using water for drinking, cooking or brushing teeth is standard Ministry of Health advice, and is recommended right across Wellington and in many other parts of New Zealand, all the time. But you can definitely collect the flushed water and use it to water house plants and flower gardens, so that it doesn’t go to waste.  

If I’m seeing blue staining or blue water, is my water safe to drink?

Regional Public Health have advised that copper leaching from household pipes is very unlikely to be a health concern, especially when taking the precaution to flush pipes. 

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

How do I clean blue staining?

Your best option is to speak with a plumber’s merchant 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, but we can't completely eliminate the issue, especially as it's about chemical reactions happening within the domestic plumbing of individual properties, which are made up of different materials, of various ages and conditions.