What Is Dezincification and How Brass Resists It

There is a failure mode that haunts plumbing systems in hard water regions — one that is completely invisible until the damage is already done. A fitting looks fine on the outside. The threads are intact. The body is solid. And then one day, under normal working pressure, it cracks. Or it starts weeping from a point that has no visible defect. Maintenance engineers arrive and find the fitting crumbles when they try to remove it — the internal metal reduced to a porous, pinkish-copper shell.

This is dezincification. And it is entirely preventable — but only if you understand what it is and specify the right material from the start.

What Actually Happens in Dezincification

Brass is fundamentally an alloy of copper and zinc — typically 60–63% copper, 35–37% zinc in standard grades. In normal conditions, this is a stable, corrosion-resistant combination. But in certain water chemistries, something selective happens: the zinc is preferentially leached out of the alloy by the water, leaving behind a copper sponge.

This selective dissolution — zinc leaving, copper remaining — is dezincification. The retained copper structure is porous, mechanically weak, and has no meaningful pressure-bearing capacity. The fitting looks like brass on the outside but has the structural integrity of a porous mineral.

The critical point: this process is slow and invisible. It can take months or years to progress to failure. During that time, the fitting passes every visual inspection. This is what makes it dangerous — and why specifying the correct brass grade from day one matters so much more than inspection alone.

What Conditions Accelerate Dezincification?

Not all water attacks brass equally. The conditions that accelerate dezincification are well-documented:

• High chloride content: Coastal water, treated mains water with chlorination, water with natural chloride deposits
• Hard water with high temporary hardness: UK water, particularly in the south of England, is notorious for this
• Elevated temperature: Hot water systems above 60°C experience accelerated dezincification rates
• Stagnant conditions: Dead legs and infrequently used branches where water sits in contact with the fitting for extended periods
• Low pH (acidic water): Below pH 7, the dissolution rate increases significantly

In practice, this means UK, Australian, and many Middle Eastern water supplies create environments where standard brass fittings are genuinely at risk. This isn't a theoretical concern — water utilities in these regions have documented dezincification as a significant maintenance issue for decades.

The Solution: DZR Brass

Dezincification-resistant (DZR) brass was developed specifically to solve this problem. The primary DZR grade is CW602N — sometimes written as CZ132 in older British standard notation. The "resistance" comes from two modifications to the standard alloy chemistry:

1. Arsenic addition (0.02–0.15%): Small additions of arsenic dramatically inhibit the dezincification mechanism. The arsenic is believed to deposit at the metal surface and block the selective dissolution pathway for zinc. It sounds counterintuitive to add a toxic element to a drinking water fitting, but the quantities are extremely small and the arsenic is bound within the alloy structure — not bioavailable in any meaningful concentration to the water passing through.

2. Controlled zinc content: DZR alloys typically have a slightly lower zinc content than standard brass, reducing the driving force for dezincification.

How to Identify DZR Brass

Responsible manufacturers mark DZR fittings with a visible indicator — most commonly a small "double chevron" symbol (») stamped or cast into the fitting body. You may also see "DZR" marked directly on larger fittings. In the UK, WRAS-approved DZR fittings will carry the WRAS mark.

However — and this is important — markings can be faked or omitted. The only reliable verification is a material certificate from the manufacturer showing the alloy composition, specifically confirming CW602N grade and the arsenic content. Any legitimate manufacturer will have this documentation. If they can't produce it, do not use their fittings in applications where DZR is required.

Where DZR is Mandatory or Strongly Recommended

• United Kingdom: WRAS (Water Regulations Advisory Scheme) requires DZR brass or equivalent for fittings in contact with mains water in most UK regions
• Australia: AS/NZS 4020 testing covers dezincification resistance; WaterMark certification requires compliance
• Germany: DIN standards for potable water fittings include dezincification resistance requirements
• Middle East: Highly chlorinated water supplies and elevated temperatures make DZR strongly advisable
• Any hot water system: Elevated temperature significantly accelerates dezincification regardless of water chemistry

The Cost of Getting This Wrong

DZR brass costs a small premium over standard CW617N — typically 5–15% more at the fitting level. Compare this to the cost of replacing 200 fittings in a completed building where access panels need to be cut, flooring lifted, and specialist labour deployed. I've seen projects where the dezincification premium avoided would have been a few thousand pounds, but the remediation cost six figures.

Specifying the right material is not a gold-plating exercise. It's basic risk management.

Testing for Dezincification Resistance

The industry test method is ISO 6509 — the standard for determining dezincification resistance of copper alloys. In this test, a section of the fitting is exposed to a copper chloride solution at elevated temperature, then cross-sectioned and examined metallographically for the depth of dezincification layer. EN13828 and WRAS both reference this test, specifying maximum acceptable dezincification depths.

When sourcing DZR fittings, ask for ISO 6509 test reports. Not generic quality certificates — the specific dezincification test data. The depth of attack should be less than 200 micrometres in the worst case.

Dezincification is not a mystery. It's a known problem with a known solution. Specify DZR where conditions warrant it, demand the test data, and move on. The fitting you put in today will still be doing its job in thirty years. That is the standard we hold ourselves to at Brassland — and the standard every specification writer should hold their supplier to.