Blue-Green stains in your bathroom?

Your water is trying to tell you something!

If you’ve started noticing blue-green streaks in your bathroom basin, toilet, bathtub or shower, don’t ignore them—they’re one of the earliest signs that your water supply is damaging your plumbing. Left untreated, this simple stain could turn into expensive leaks, pipe failures, and major repairs.

This issue is becoming increasingly common in homes that rely on rainwater tanks. As more properties switch to polyurethane water tanks and metal roofing, we’re seeing a rise in corrosive water conditions—especially where water isn’t being naturally neutralised.

Why Rainwater Becomes Corrosive​

Pure rainwater is naturally acidic. While neutral water sits at pH 7.0, typical rainwater has a pH around 5.6. Concrete tanks help buffer this acidity because the lime within the concrete neutralises the water. Polyurethane tanks, however, offer no such protection.

This means acidic rainwater flows straight into your home’s copper pipework. Over time, this begins dissolving the copper from inside the pipes—what we call soft metal corrosion. The dissolved copper then shows up as a blue-green stain on your ceramics. If you’re seeing stains, the corrosion has already begun.

And once corrosion starts, the risk of leaks, pinhole failures, and water damage skyrockets.

What makes rain water corrosive?

A variety of factors influence whether water will attack the metal in your plumbing. Here’s what’s happening behind the scenes:

Water + Metal = Corrosion

All metals can corrode, but the rate depends on how aggressive the water is.

• Most at risk: mild steel, copper, brass
• Least at risk: stainless steel

Brass—which contains copper, zinc, and lead—can leach these metals back into the drinking water. This is why the “first flush” of water from a brass tap may contain elevated metal levels. If you know your water is corrosive, you should always let taps run for a few seconds before using the water for drinking or cooking.

Blue-Green Staining = Copper Loss

Those stains on your shower tiles or sink are copper being stripped from your pipes or hot water system. Over time, this leads to pitting corrosion, which creates tiny holes in the pipe walls. These pinholes eventually leak and can cause significant structural or water damage.

Low pH Accelerates Corrosion

When water drops below pH 7, it becomes acidic—and therefore corrosive.
Hardness and alkalinity can buffer some of this acidity, but low-pH water dissolves the protective calcium carbonate layer that should form inside pipes. Without that protective scale, the metal is exposed and vulnerable.

Dissolved Gases Make It Worse

Certain gases found in rainwater intensify the corrosion process:

• Carbon dioxide forms carbonic acid, lowering pH further.
• Hydrogen sulphide contributes to galvanic corrosion and pitting.

These reactions create the perfect environment for long-term pipe damage.

Confirming the Problem: Why a Water Analysis Matters

While blue-green staining is a strong visual clue, the only way to confirm corrosive water is through a comprehensive water analysis. Testing identifies your water’s:

• pH
• alkalinity
• hardness
• dissolved metals
• corrosive or scale-forming tendency

Pristine Water Systems uses recognised corrosivity indices and physical measurements to determine how aggressive your water is—and what’s causing it.

Protecting Your Home: Solutions That Work

If you’ve noticed staining, don’t wait. Corrosion only gets worse with time.

Your local Pristine Water Systems technician can analyse your water and recommend the right system to protect your plumbing. For most homes with acidic rainwater, calcite filters are a reliable and popular solution. They raise the pH, neutralise acidity, and help prevent ongoing copper corrosion.

However, pH correction is only part of the job. You may also need to address:

• Sediment from roofs and tanks
• Bacteria introduced from animal droppings or decomposing pests
• Tank hygiene issues

Pristine Water Systems offers complete treatment options tailored to your home, water source, and usage.

Don’t Ignore the Stains—Your Pipes Are Warning You

If you’re seeing blue-green streaks anywhere in your bathroom or kitchen, it’s time to act. Corrosive water won’t fix itself, and the longer it’s left, the more damage it creates.

Book an assessment with your local Pristine Water Systems operator today or contact us online. Protecting your water quality now could save you thousands in plumbing repairs later.