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Blue - Green Copper Staining

What does it look Like?

In rare and specific situations, the installation of a water softener may highlight the unsightly presence of blue-green stains in areas where softened water is used. These stains are most noticeable around leaking taps and on the inner edge of toilets.

The immediate reaction, understandably, is to question if it is the water softener causing it.  

The short answer is no, but it can highlight the issue.

Luckily, copper staining is not a common occurrence and is usually temporary. 

Softened water is generally gentle and has a neutral pH. 

However, approximately 1% of households that start using softened water may encounter the challenge of stubborn blue-green stains on bathroom fixtures, which can be quite bothersome to remove.


What causes it?

Blue or green staining occurs with copper pipework and fittings (including brass, which is copper + zinc), and is caused by the corrosion and dissolution of the metal itself. 

The result is that whatever is causing it adds excessive amounts of dissolved copper to the water. When the copper-laden water is allowed to sit, it begins to stain. Unsurprisingly, the water may also have a metallic taste to it.

Water Quality 

Acidic Water (< 6.5 pH)

Acidic water quality (Low pH) is a common cause.

The pH of drinking water is not regulated, but it is recommended that pH levels fall between 6.5 and 8.5.  This is classed as Neutral pH, and is right in the middle of the scale.

Naturally soft water (such as is found in Scotland and Cornwall) is considered aggressive and has a lower pH, and ion-exchange softened water often also gets associated as being aggressive.  In fact, this is not normally the case.  The reason they get linked is because of the word association of soft / softened water.  Softened water is normally akin to hard water on the pH scale.

Basic Water (> 8.5 pH)

Water with a high pH isn't quite as problematic as water with low pH, but does have its issues. Among them is hard water - water with high levels of minerals (mainly calcium and magnesium). Hard water typically has a high pH because the minerals in the water buffer against acidification.

Water with a high pH might taste slightly bitter, and is not known to have any effects on health - for good or bad. So the next time you see a bottle of "super-hydrating" alkaline water in the shops, save your money - the science doesn’t support the marketing hype.

Stray electrical currents

Improper electrical grounding can also hasten corrosion (this happens when stray electrical current runs through the plumbing system).  The latter can occur when an older home's plumbing is incorrectly used as a ground for the home's electrical system.

It can be difficult to determine if electrolysis (known as an electrochemical process) is behind copper leaks and staining, but because it is uncommon, hold off calling an electrician until other possibilities have been ruled out. 

However, if you experience other electrical issues or get a shock when touching pipes, that should clearly be addressed with urgency.  Water and electricity can be disastrous! 

Poor Copper quality

Increasingly, reports of copper staining is also found to occur in properties where inferior copper (in the UK, this is typically imported from China) has been used. 

If the discolouration is isolated to specific areas of the home, it indicates that those areas likely contain inferior copper. In such cases, it may be advisable to replace the copper in the affected areas with high-quality British copper, such as Yorkshire Copper. If the entire home is affected, it becomes a larger problem.

The problem arises from residues of copper oxide dissolving into the water. These residues form on the surfaces of pipes during the manufacturing and storage processes. 

Usually, after a few weeks of use and thorough flushing of the pipework, the occurrence of staining significantly reduces and eventually disappears. However, in some rare cases, the problem can persist - we refer to this as Persistent Copper Staining.


The Theory surrounding Persistent Copper Staining:

There are various theories regarding the cause of persistent copper staining, with one possibility being a reaction between dissimilar metals and softened water within the plumbing system. In almost all cases, the level of interaction is minimal and unlikely to leave permanent staining.

What can you do about it?

Check your Earth Bonding

Faulty or improperly connected electric "earth" cabling in the property can worsen copper staining issues. 

Earth strapping is typically attached above the incoming water main stopcock. 

It is essential to ensure that all earth bonding straps are firmly connected. As more plastic pipes are used now in properties, it’s important to ensure that copper straps connect to copper straps, without plastic becoming an insulator.

Other earth straps may also be present, such as those connected to toilet pipework and in the bathroom. Seeking advice from a professional electrician is recommended in such cases.

Blending the Water

You could try partially blending the softened water with hard water to neutralise the reaction. 

Some softeners have a blending valve, or alternatively, the bypass valve can be adjusted to achieve a water mix. The blend should be subtle, measuring no more than 30 to 40 mg/l of carbonate hardness. 

There is also a blending valve kit that can be fitted to the pipework which gives a more accurate level of control (product D1746).  

Blending the water will result in water that is not completely softened, but is still softer than naturally soft water.

Increase the backwashing cycle

We don’t know yet if this will help reduce the problem, but we are currently doing research in a couple of isolated cases to see what effect this change might make.  

Fitting an acid neutraliser unit

This small device can be inserted into the outlet hose of the water softener. The dosing unit contains depleting media that needs to be replaced from time to time, and essentially increases the hardness of the water, so it’s important to watch you don’t add too much hardness back in to the supply.

The media creates a thin protective film inside the pipes. This film can prevent aggressive reaction from occurring.  

In the USA, they suggest fitting a unit like this before a water softener - this reinforces the industry view that softened water is not the culprit!

Water Testing for low pH

Water that has a pH of 6.8 or less is considered aggressive and can cause damage to metal surfaces that it comes into contact with. The lower the pH, the more acidic the water. The theory is that each .10 of a point below is exponentially more corrosive.

If you wanted to test your water, you could purchase widely available pH test strips (try the aquarium section of a pet store or your hot-tub / pool supplier). These strips aren't anywhere near as accurate as lab-grade electrode testers, but will give you a decent indication of your water quality. 

A laboratory water test will, however, be more accurate and tell you if your water is outside the normal pH range of 6.5-8.5, and whether there is copper in the water (and other minerals such as lead or iron).


What can you do about it?

White vinegar is rightly touted as an excellent cleaning tool, and with the addition of salt, may be able to get rid of the blue/green stains.

Try dissolving a tablespoon of salt in a cup of warm vinegar, soaking a rag with the solution, and letting it sit on the stain. The stain may begin to lift immediately - if not, try lightly scrubbing with the rag, and repeat the process if necessary. Because vinegar is a relatively weak acid and the salt is dissolved, this should be safe for many fixture materials, but if in doubt, test a small hidden area first!

Will it happen in my home?

Unfortunately, there is no way to predict if copper staining may occur in a home. As it is more of a cosmetic issue than a serious technical problem, there are very few reported cases, and therefore, no extensive studies have been conducted to investigate the possible causes.

 In general, it is believed that although copper staining can be annoying, it does not cause any long-term damage to a household water system. 

 The methods mentioned above should help control and eliminate copper staining in the majority of cases.