What Is Dezincification and How Brass Resists It

There is a failure mode that haunts plumbing systems wherever the water is aggressive to brass — 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 — the standard grades CW614N and CW617N contain 57–59% copper, about 39–40% zinc and 1.6–3.5% lead. 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 — above all in relation to the carbonate (temporary) hardness: this is the relationship plotted in Turner's diagram (1961), still the standard first assessment of a water. Plenty of chloride with little carbonate hardness is the dangerous combination; coastal and desalinated supplies are typical cases
• Soft water with low alkalinity, and water above about pH 8: poorly buffered waters — typical of Scandinavia and of upland sources — attack the zinc-rich phase; at pH 8–9 the attack takes the "meringue" form, with bulky white zinc corrosion products that block hot-water fittings. A high carbonate hardness, by contrast, tends to protect brass
• 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

In practice, this means parts of the UK, Scandinavia, Australia and many Middle Eastern supplies create environments where standard brass fittings are genuinely at risk. This isn't a theoretical concern — it is the reason these markets wrote dezincification resistance into their plumbing rules decades ago.

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 alloy chemistry and from a heat treatment:

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 arsenic to a drinking water fitting, but the quantities are very small, and metal release from drinking-water alloys — arsenic included — is exactly what is tested before an alloy is accepted for drinking water: a composition is listed only after a long-term metal-release test (EN 15664-1).

2. Controlled zinc content: DZR alloys have a slightly lower zinc content than standard forging brass (CW602N: 61–63% copper), which keeps the zinc-rich beta phase to a minimum.

3. Heat treatment: Arsenic only protects the alpha phase. After hot working, DZR brass is therefore heat-treated so that any remaining beta phase is broken up into isolated islands instead of forming a continuous path into the metal. This is why the test is carried out on the finished product and not only on the bar — and why "CW602N" on a drawing should be accompanied by the dezincification requirement.

How to Identify DZR Brass

Dezincification-resistant fittings are usually marked: in the UK with the letters "CR" (corrosion resistant) or "DZR" forged or stamped into the body, in Australia and New Zealand with "DR". A WRAS or WaterMark approval, where the product has one, is listed under the approval holder's name in the scheme's public directory.

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: the Water Supply (Water Fittings) Regulations 1999 require any concealed water fitting that is not a terminal fitting to be made of gunmetal or another dezincification-resistant material — which is why DZR brass is the norm for buried and built-in fittings
• Australia: copper-alloy fittings in contact with water must be dezincification resistant to AS 2345 (marked "DR"); this is part of the product standards, such as AS 3688, against which WaterMark certification is granted. Since 1 May 2026 new products for drinking water must in addition be lead free — weighted average lead not more than 0.25 % (National Construction Code 2022, Volume Three) — a limit the leaded DZR grade CW602N does not meet. (AS/NZS 4020 is a different test — the effect of a product on water quality)
• Scandinavia: the water is soft, with low alkalinity, and dezincification-resistant brass is the established requirement of the national type-approval schemes — CW602N is the brass most commonly installed
• European Union: from 31 December 2026 the European positive list (Implementing Decision (EU) 2024/367) decides which alloys may be in contact with drinking water. The lead-free, dezincification-resistant silicon brass CW724R is on it; the leaded DZR grades CW602N and CW625N are not — compositions approved nationally between 13 July 2021 and 31 December 2026 may still be used until 31 December 2032
• Middle East: Soft, low-mineral desalinated 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 modest premium over standard CW617N. Compare this to the cost of replacing fittings in a completed building, where access panels need to be cut, flooring lifted and specialist labour deployed: the remediation bill is typically many times the value of the fittings themselves.

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 6509-1 — 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. The test produces a depth, not a verdict: the acceptance limit comes from the material or product standard that calls up the test.

When sourcing DZR fittings, ask for ISO 6509-1 test reports. Not generic quality certificates — the specific dezincification test data. For CW602N, EN 12164 (rod) and EN 12165 (forging stock) allow a maximum depth of 100 micrometres in any direction; the 200-micrometre limit belongs to the aluminium-bearing DZR grades CW625N and CW626N. Check that the report names the alloy and the limit it was assessed against.

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 every specification writer should hold their supplier to — and the reason we machine DZR components from certified CW602N with an EN 10204 3.1 certificate, and arrange ISO 6509-1 test evidence through an external laboratory when the order calls for it.

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Sources & references

Corrosion references:

Last reviewed: September 2026. Standards and regulatory references are checked at each review.