Blue-green stains on sinks, showers, toilets and plumbing fixtures are most commonly caused by copper. When copper dissolves from pipes, valves or other components, it can react with substances in the water and form characteristic blue-green deposits. The issue is relatively common in properties with copper plumbing, particularly where water chemistry promotes corrosion.
The colour results from the same fundamental chemistry responsible for the green patina that develops on old copper roofs, statues and copper surfaces. Low pH, low alkalinity, very soft water or otherwise aggressive water chemistry can increase copper dissolution. In some cases, nickel, which is present in many alloys and stainless materials, may also contribute to green colouration if corrosion occurs under unfavourable conditions.
Did You Know?
The same copper compounds that create blue-green stains in bathrooms are responsible for the green colour of many historic copper roofs around the world. The colour develops when copper reacts with oxygen, carbon dioxide and other substances in its environment, forming a protective patina. In drinking water systems, similar colours often indicate that water chemistry or corrosion conditions should be investigated.
Common Causes
- Corrosion of Copper Pipes
- Low pH
- Low Alkalinity and Buffer Capacity
- Very Soft or Aggressive Water
- Corrosion of Nickel-Containing Alloys
- Long Water Stagnation in Pipe Systems
Common Symptoms
- Blue-Green Stains in Sinks and Toilets
- Discolouration Around Plumbing Fixtures
- Metallic Taste
- Elevated Copper Concentrations
- Most Visible Where Water Evaporates
Common Treatment Methods
- Water Analysis
- Assessment of pH and Alkalinity
- Remineralization or pH Adjustment
- Inspection of Corrosion Issues
- Replacement of Damaged Components if Necessary
Example Treatment Trains
Water Analysis
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pH Adjustment
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Remineralization
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Reduced Corrosion
Water Analysis
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Pipe System Inspection
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Corrosion Mitigation
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Normal Operation
Blue-green stains are most commonly associated with copper and often indicate that metals are dissolving from plumbing systems. If the issue appears suddenly or increases over time, water analysis and evaluation of pH, alkalinity and corrosion conditions are recommended. Early identification can help protect both infrastructure and water quality.