Blue-green staining from copper pipes — what causes it and what to do

What causes blue-green staining

Blue-green staining around taps, in sinks, on bath surfaces, or on shower screens has one cause: copper dissolving from copper plumbing pipes or brass fittings into the water. When copper ions dissolve into water and then contact a surface — or when that water dries and the copper oxidises — it leaves the distinctive blue-green colour of copper oxide or copper carbonate. The same chemistry gives the Statue of Liberty its patina.

The staining itself is not the problem. It is a symptom. The underlying issue is corrosive water chemistry that is actively dissolving metal from your plumbing. Understanding why it is happening is necessary to know whether it is self-resolving, manageable, or requires action.

The three main causes in Australian homes

1. Low pH (acidic water) — the most common cause

Water with a pH below 7.0 is acidic and corrodes copper more aggressively than neutral or slightly alkaline water. When acidic water sits in contact with copper pipe for extended periods — overnight, during weekends, after holidays — it dissolves copper ions into the standing water. The first water out of the tap in the morning often has the highest copper concentration for this reason.

In Australian mains water, pH is typically well-managed and sits comfortably above 7.0 in all capital cities. The blue-green staining risk from mains water is generally low for this reason — though a small proportion of homes experience it due to localised plumbing conditions, nearby infrastructure, or electrical earthing issues.

The significant exception is rainwater tank systems. Rainwater is naturally low in buffering capacity (alkalinity) and typically has a pH of 5.5–6.5. When collected rainwater with pH 6.0 sits in copper plumbing overnight, the copper dissolution rate can be dramatically higher than from mains water. Blue-green staining is considerably more common in homes with copper plumbing on rainwater tank supply than on mains.

2. New copper plumbing — usually self-resolving

New copper pipes sometimes produce a temporary blue or green tinge to water as the inside surface is new and smooth, without the natural protective oxide patina that forms with age. As the copper surface oxidises and forms a protective film — typically over 6–12 months of normal use — the dissolution rate decreases significantly. If you have recently had copper plumbing installed and are seeing mild staining or slightly coloured water, this is the most likely explanation and is usually self-resolving.

3. High chloride levels or electrochemical reactions

High chloride concentrations in water increase its electrical conductivity and can accelerate copper corrosion. Coastal properties or areas with high groundwater salinity can experience this. Electrochemical reactions from electrical earthing through copper pipes can also contribute to accelerated corrosion in some installations.

Is blue-green staining a health risk?

The staining itself is not harmful — it is an aesthetic issue. The copper in the water that causes it may or may not be at levels of concern depending on severity. The ADWG health guideline for copper in drinking water is 2 mg/L. Visible blue or blue-green staining on sink surfaces generally begins to occur at copper concentrations above 1 mg/L.

For healthy adults, copper at 1–2 mg/L in drinking water is unlikely to cause harm given average daily water consumption. Copper is an essential trace element — we need small amounts from food and water daily. The concern at elevated concentrations is gastrointestinal effects (nausea, vomiting) at acute high doses, and longer-term liver effects with chronic very high exposure.

Two groups are more sensitive:

• Infants: More vulnerable to copper toxicity due to immature liver function for excreting excess copper. If you are seeing significant blue-green staining and have infants at home, use filtered or bottled water for formula and infant drinking water until the issue is resolved.
• People with Wilson’s disease: A rare genetic condition that impairs the body’s ability to excrete copper. Elevated dietary copper including from water is a genuine concern for this group.

pH in Australian cities — the mains water context

All Australian capital cities treat mains water to a pH well within the ADWG guideline range of 6.5–8.5 — and generally above 7.0 specifically to reduce corrosivity to plumbing. This is why significant blue-green staining from mains supply copper plumbing is uncommon in Australian homes.

The contrast with rainwater tanks (pH 5.5–6.5) is stark. Tank water with pH 6.0 is in a range where copper corrosion is significantly elevated compared to mains water at pH 7.4. Homes that converted from mains supply to a rainwater tank and have copper plumbing should monitor for this issue.

What to do if you have blue-green staining

Practical steps

• Run the tap before using: Let cold water run for 30–60 seconds before using water that has been standing in pipes (first thing in the morning, after returning from holiday). This flushes stagnant water that has been in contact with copper overnight.
• Never use hot tap water for drinking, cooking or formula: Hot water dissolves metals from fittings far faster than cold. Always start with cold and heat it separately.
• Get the water tested: A NATA-accredited lab test for pH, copper, and alkalinity costs approximately $60–$100. This tells you the driver of the corrosion and whether levels are concerning.
• pH correction filter (for rainwater tanks or persistently acidic water): A calcite neutralising filter raises pH by dissolving calcium carbonate into the water as it passes through. This increases the pH to approximately 7.0–7.5 and dramatically reduces copper dissolution. This is a point-of-entry (whole-home) system that treats all water entering the property.
• Point-of-use RO or NSF 53 certified carbon (for drinking water): For kitchen tap use specifically, an RO system removes dissolved copper from drinking water regardless of source. This addresses the health concern for drinking and cooking while you resolve the underlying plumbing issue.
• Plumber assessment for persistent or severe cases: If staining is heavy, you have pinhole leaks, or the water is visibly coloured, a licensed plumber can assess the plumbing condition and the feasibility of descaling or partial pipe replacement. In older homes where lead solder was used in copper plumbing, this assessment may also reveal lead risk.