Water problem
Low pH and blue-green stains
Acidic water dissolves copper from the pipes it passes through. The blue-green stain is the copper, which means the plumbing itself is being consumed.
What you might notice
- Blue-green staining in sinks, tubs, and around fixtures
- A metallic taste
- Pinhole leaks appearing in copper pipe
- Green deposits at joints
The stain is dissolved pipe
Blue-green marks below a tap or around a bath waste are copper. Acidic water is dissolving the inside surface of the copper pipework it travels through, and what you are looking at is that metal deposited where the water evaporates.
That makes this different from a cosmetic complaint. The staining is a symptom of the plumbing being consumed from the inside, and the end point is pinhole leaks, typically appearing in hot water lines first because heat accelerates the reaction.
Water below roughly pH 6.5 is considered corrosive. It is common on private wells in areas with granite bedrock and thin soils, where there is little natural carbonate to buffer the rainwater.
Confirming it properly
A pH strip or meter gives an immediate reading and costs very little. A laboratory copper test confirms how much metal is actually being picked up, which is the number that tells you how urgent this is.
Sample first thing in the morning, before any water has been used. Water that has sat in the pipes overnight has had the longest contact time and will show the highest copper concentration, which is the exposure that matters.
On municipal water this is unusual. Utilities adjust pH and add corrosion inhibitors specifically to prevent it, because the same chemistry that dissolves copper also dissolves lead. If you are on public water and seeing blue-green staining, tell the utility, because it is information they need.
Correcting it, and the knock-on effect
A calcite neutraliser raises pH by dissolving crushed limestone into the water. It is simple, it has no moving parts beyond a backwash valve, and the media is topped up rather than replaced because it is consumed by design.
The side effect is that dissolving calcium raises hardness. Where you also have a softener, it now has more work to do, so the two have to be sized together with the neutraliser first in the sequence.
Before treating the whole supply, check whether the staining appears at every fixture or just one. A single stained basin is often a failing washer or a corroding fitting rather than the water, and replacing a tap is considerably cheaper than treating a building.
How to confirm it
A pH test gives an immediate reading. Below about 6.5 is corrosive. A copper test confirms the metal is being dissolved. Both are standard lines on a well water panel. On public water this is unusual, because utilities control pH at the plant.
The test that settles this is ph meter or strip, plus a laboratory copper test. We include what we can measure on site in a free water test, and we will tell you plainly when a certified laboratory is the right next step rather than anything we can do at your kitchen tap.
When not to treat it
Blue-green staining in a single fixture is often a failing washer or a fitting rather than the water. Check whether it appears throughout the property before treating the whole supply.
Treatment options that actually apply
These are the equipment types that address this problem. Each page states what the equipment does not do, so you can rule it out quickly if your situation does not match.
- Acid neutralisers. A calcite or magnesia bed that raises the pH of acidic water, which stops it dissolving copper out of the pipes it runs through.
- Well water systems. A treatment train assembled around a current laboratory test, in stages.
What none of these will do
- Copper already dissolved into the water upstream of the unit.
- Existing blue-green staining, which needs cleaning separately.
- Bacteria, nitrates, or organic contaminants.
Getting it installed
Once a test has confirmed the problem and narrowed the equipment, the practical questions are access, space, and whether anyone's permission is needed. Those are covered on the installation pages, along with what a visit involves and how long it takes.
- Free water testing. 45 to 60 minutes.
- All installation services
- What installation costs
Other water problems
Sources
- Secondary Drinking Water Standards. US Environmental Protection Agency, 2024.
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