Brass does corrode in water, but not in the straightforward way iron rusts. Instead of dissolving uniformly, brass undergoes a sneakier process in which zinc is selectively pulled out of the alloy, leaving behind a weak, spongy layer of copper. This signature form of degradation, called dezincification, can hollow out plumbing fittings and valves from the inside while the surface still looks intact. How fast it happens depends on the water’s chemistry, the brass alloy’s composition, temperature, and whether other metals are in the picture.
How Brass Actually Breaks Down in Water
Brass is not a single metal; it is an alloy of copper and zinc, sometimes with small additions of lead, tin, or arsenic. When brass sits in water, the zinc atoms are more chemically reactive than the copper atoms. Zinc dissolves preferentially into the water, and what stays behind is a porous residue of metallic copper along with some copper compounds. This residue looks reddish or pinkish compared to the original yellow brass, and it is structurally fragile. A pipe fitting that has been heavily dezincified can crack under pressure that the original alloy would have handled easily.
Researchers have confirmed that zinc dissolution happens under a wide range of conditions. Spectroelectrochemistry work has shown that selective dissolution of zinc occurs even at modest electrochemical potentials, and as conditions become more aggressive, copper starts dissolving too, though the zinc-to-copper ratio in dissolved material remains skewed toward zinc.1ECS Meeting Abstracts. The Dezincification of Brass: In Situ Measurement of Zn and Cu Dissolution with Atomic Emission Spectroelectrochemistry The copper left behind does not simply re-plate onto the surface in a neat layer. It forms a mixture of metallic copper and insoluble copper compounds that gives dezincified brass its characteristic weak, crumbly texture.2Full Text Book of Minar Congress 6. Characterizations of Precipitated Zinc Produced by Dezincification of Brass Waste in HCl Solution
Why Some Brass Alloys Corrode Faster Than Others
Not all brasses are created equal. The internal structure of a brass alloy plays a huge role in how quickly it gives up its zinc. Brass with a higher proportion of what metallurgists call the beta phase, a zinc-rich crystal structure, corrodes faster because that phase is less thermodynamically stable in water. A study comparing three commercial brasses with different beta-phase fractions found that the alloy with the most beta phase had the most negative corrosion potential, the lowest resistance to current flow through the corroding surface, and the highest zinc leaching rate over a 201-day immersion test.3PubMed. Selective dissolution of zinc and lead from duplex β-phase brasses in low and high conductivity water
In practical terms, this means that brasses with more than about 35 percent zinc tend to contain significant amounts of beta phase and are more vulnerable. Alpha brass, which has lower zinc content and a more stable crystal structure, is softer and more ductile but resists corrosion much better. Historical analysis of brass artifacts recovered from shipwrecks has confirmed that alpha brass, with zinc up to about 35 percent, maintains good corrosion resistance even after extended immersion.
The total zinc content is a useful rule of thumb, but the real story is about microstructure. Two brasses with identical overall zinc percentages can behave differently if one was heat-treated or cold-worked in a way that changed the distribution of alpha and beta grains. When shopping for brass components intended for water service, the alloy designation matters more than any single number.
Water Chemistry That Speeds Things Up
The water itself is often the deciding factor. Several chemical characteristics push brass corrosion from slow background noise to a real engineering problem.
- Chloride concentration: Chloride ions are particularly aggressive toward brass. Research on alpha brass in buffered solutions showed that chloride ions promote both dezincification and pitting corrosion, with susceptibility depending on chloride concentration and the nature of the passive layer already on the metal surface.4Materials and Corrosion. Passivation and pitting corrosion of α‐brass (Cu/Zn: 63/37) in neutral buffer solutions containing chloride ions Seawater, brackish groundwater, and even heavily chlorinated tap water all carry meaningful chloride loads.
- Dissolved oxygen: Oxygen in water drives the cathodic half of the corrosion reaction. At the brass surface, dissolved oxygen accepts electrons released when zinc dissolves, completing the electrochemical circuit and allowing corrosion to continue.5e-Journal of Surface Science and Nanotechnology. Effect of Oxygen Bubbling on the Dissolution of Brass in Acidified Sodium Sulfate Solution under Free Corrosion Conditions Stagnant water with low oxygen may corrode brass less aggressively than turbulent, well-aerated water, all else being equal.
- Low alkalinity and soft water: Water that is low in dissolved minerals and alkalinity tends to be more corrosive toward metals generally. Field investigations in regions with soft, low-alkalinity water have documented significant metal leaching from brass plumbing.6PubMed. Corrosion control in water supply systems: effect of pH, alkalinity, and orthophosphate on lead and copper leaching from brass plumbing
The interplay between these factors is not always intuitive. Adjusting pH upward, which you might expect to help, does not always reduce corrosion. One laboratory study of plumbing systems found that pH-alkalinity treatment actually made metal leaching worse in standing water samples from brass faucets compared to untreated controls.7Canadian Journal of Civil Engineering. The effect of zinc orthophosphate and pH-alkalinity adjustment on metal levels leached into drinking water Water chemistry is a package deal, and changing one variable without accounting for the others can backfire.
Temperature and Flow Make a Big Difference
Heat accelerates brass corrosion substantially. Detailed studies of brass in concentrated salt water have shown that the rate of alloy dissolution climbs with both temperature and salt content. At lower temperatures and lower salt levels, zinc and copper dissolve at roughly similar rates without dramatically changing the surface composition. But at 60°C and 80°C with high salt concentrations, severe dezincification sets in: the surface becomes almost entirely copper, with copper making up roughly 95 to 98 percent of the alloy’s outermost layer.8Corrosion. Dezincification of Brass in Hot, Concentrated Salt Water This is why brass heat-exchanger tubes in cooling systems, desalination plants, and marine engines are classic trouble spots.
Flow velocity introduces another dimension. When water carrying sand or other particles moves quickly past a brass surface, the combined effect of erosion and corrosion is worse than either alone. Research on aluminum-brass alloys found that jet velocity had a greater effect on corrosion rate than the concentration of suspended particles, because higher velocity increases both how often particles strike the surface and how much energy each strike delivers.9Materials and Corrosion. Corrosion behavior of Al‐brass alloy during erosion–corrosion process: Effects of jet velocity and sand concentration Any protective film that forms on the brass gets scrubbed away faster than it can rebuild, leaving fresh metal exposed to the corrosive water.
Galvanic Corrosion From Mixed Metals
When brass is physically and electrically connected to a different metal in the same water, galvanic corrosion can make things worse for one of the two. In a brass-steel couple, the brass acts as the cathode (the “noble” partner) and the steel dissolves faster than it would on its own. Polarization studies have shown that brass containing more than about 40 percent copper behaves essentially like pure copper in these couples, while lower-copper brass alloys behave more like zinc.10CORROSION. Polarization Studies of Brass-Steel Galvanic Couples So the brass side may survive reasonably well, but the steel corrodes faster.
That picture can flip in other configurations. If brass is paired with a more noble metal like stainless steel or titanium, the brass becomes the sacrificial partner and corrodes preferentially. Even within a single piece of brass, the beta-phase grains are less noble than the alpha-phase grains, creating tiny internal galvanic cells that drive dezincification at the microstructural level. Failure analyses of admiralty brass heat-exchanger tubes have documented dezincification occurring specifically under deposits as a result of galvanic corrosion, where the deposit creates a small oxygen-depleted zone next to aerated metal.11ASM Failure Analysis Case Histories: Power Generating Equipment. Stress-Corrosion Cracking and Galvanic Corrosion of Admiralty Brass
The practical lesson is straightforward: avoid connecting brass directly to steel, aluminum, or iron in water without an insulating joint. And be aware that any place where deposits, barnacles, or biofilms accumulate on brass can create localized galvanic conditions even with no second metal involved.
When Bacteria Join In
Brass has a well-deserved reputation for antimicrobial properties on dry surfaces, but submerged in water, bacterial communities can colonize it and accelerate corrosion. Sulfate-reducing bacteria are the main culprits. These organisms thrive in low-oxygen conditions underneath biofilms and produce sulfides as a metabolic byproduct. Those sulfides react with the copper and zinc in brass, creating conditions ripe for pitting. Investigations of copper alloys in saline water have found that pits developed under mixed bacterial communities and that the localized corrosion arose from a combination of oxygen-depleted zones, concentrated chlorides within the pits, and the direct reaction of base metals with bacterially produced sulfides.12CORROSION. Microbiologically Influenced Corrosion of Copper Alloys in Saline Waters Containing Sulfate-Reducing Bacteria
Microbially influenced corrosion is often overlooked because the biofilm hides the damage underneath. By the time a brass component fails, the pitting can be deep and widespread. This is most relevant in cooling water systems, fire sprinkler networks, and industrial piping where water sits for long periods and bacterial colonies have time to establish themselves.
What Brass Corrosion Means for Drinking Water
For most homeowners, the question about brass and water is not about structural failure but about what ends up in the glass. Brass plumbing components, especially faucets, valves, and water meters, leach metals into the water they contact. The corrosion of brass releases not just zinc and copper but also lead, because many traditional brass formulations contain a small percentage of lead to improve machinability.
Laboratory research has found that new brass faucets can contribute lead to drinking water above action levels, with roughly 60 to 75 percent of the leached lead appearing in the first small volume of water drawn from the faucet.13Journal AWWA. A Laboratory Study of the Leaching of Lead From Water Faucets This “first-draw” effect is why public health agencies recommend running the tap for a few seconds before drinking, especially in the morning or after the water has been sitting for hours. Studies of commercially available brass water meters have confirmed high rates of lead, copper, and zinc release during the first few days of use, driven by both general corrosion and internal galvanic corrosion between different phases in the brass.14PubMed. Release of lead, copper, zinc from the initial corrosion of brass water meter in drinking water
Field studies in regions with soft, low-alkalinity water paint a concerning picture. An investigation of brass plumbing in the Auckland area of New Zealand found that more than 90 percent of unflushed water samples contained lead above the country’s maximum acceptable value of 10 micrograms per liter.6PubMed. Corrosion control in water supply systems: effect of pH, alkalinity, and orthophosphate on lead and copper leaching from brass plumbing The water supply there was characterized as soft and potentially corrosive, with low hardness and alkalinity. Similar conditions exist in many other regions, including parts of the Pacific Northwest, Scandinavia, and the Scottish Highlands. If your water utility reports low hardness and alkalinity, your brass fixtures deserve extra attention.
The good news is that corrosion inhibitors can help. Zinc orthophosphate, added at the water treatment plant, has been shown to reduce lead and copper leaching from plumbing systems below the levels seen in untreated water.7Canadian Journal of Civil Engineering. The effect of zinc orthophosphate and pH-alkalinity adjustment on metal levels leached into drinking water Many water utilities in North America and Europe use phosphate-based corrosion inhibitors as part of their treatment program specifically to limit lead and copper at the tap.
Dezincification-Resistant Brass and Other Protective Strategies
Engineering responses to brass corrosion have evolved considerably. The most direct solution is to use a brass alloy specifically formulated to resist dezincification. DZR (dezincification-resistant) brass contains small additions of arsenic or other elements that stabilize the alloy and prevent the selective leaching of zinc. These alloys are marketed for water-system applications, marine hardware, and anywhere brass will be in prolonged contact with water.15Alloy Digest. DZR YELLOW BRASS In many countries, building codes now require DZR brass for buried or embedded plumbing fittings. If you are replacing valves or fittings in your home and the old components show signs of pink discoloration or unusual brittleness, DZR brass is the replacement to ask for.
On the industrial side, chemical inhibitors applied to cooling water systems provide another line of defense. Azole-based inhibitors such as benzotriazole form a thin protective film on the brass surface that slows both general corrosion and dezincification. Electrochemical studies have compared benzotriazole with newer proprietary azole formulations for passivating brass heat exchangers, finding that the protective film can be maintained effectively as part of a phosphate-based water treatment program.16CrossRef API / CORROSION 2010. Optimization of Cooling Water System Passivation of Brass Alloys in Petrochemical Facilities These programs are standard practice in petrochemical plants, power stations, and large HVAC systems where brass heat exchangers handle thousands of gallons per hour.
For homeowners who cannot swap out all their brass fixtures or control what their water utility does, a few practical steps help. Flushing the tap for 15 to 30 seconds before filling a glass clears the most metal-laden stagnant water. Point-of-use filters certified for lead removal catch what flushing misses. And if you are on a private well with soft, acidic water, a whole-house treatment system that raises pH and adds alkalinity can slow corrosion across every metal surface in the plumbing.
Pitting Versus General Corrosion
Dezincification is the headline story for brass in water, but it is not the only form of attack. Pitting corrosion creates small, deep holes that can penetrate a brass wall while the surrounding surface remains mostly intact. This makes pitting harder to detect and, in some ways, more dangerous structurally than dezincification, which at least spreads the damage over a larger area.
Chloride ions are a key trigger. In buffered solutions without chloride, brass tends to undergo dezincification at high electrochemical potentials but does not pit. Add chloride, and pitting becomes a real possibility depending on the nature of the passive layer already present.4Materials and Corrosion. Passivation and pitting corrosion of α‐brass (Cu/Zn: 63/37) in neutral buffer solutions containing chloride ions The passive layer on brass is not as robust as the oxide films on stainless steel or titanium. It can be breached locally by chloride, and once a pit initiates, the chemistry inside the pit becomes more acidic and more chloride-rich than the surrounding water, making the pit self-perpetuating.
Bacterial biofilms compound the problem. The sulfide-producing bacteria discussed earlier tend to create pitting beneath their colonies because the biofilm traps aggressive chemistry against the metal. In marine and industrial settings, pitting under biofilms is one of the most common failure modes for brass components. Inspectors often find apparently sound brass tubes with pinhole leaks that turn out to sit beneath a thin crust of biological growth.
Reading the Signs of Brass Corrosion
If you have brass plumbing or fittings at home, a few visual and practical clues can tell you whether corrosion is active. A pinkish or reddish hue on a normally yellow brass surface is a strong sign of dezincification; you are seeing the copper skeleton left behind after zinc has dissolved. White or greenish crusty deposits around threaded fittings can indicate zinc or copper corrosion products precipitating out of solution. Brass that feels unusually soft, chalky, or crumbly when you handle it has likely lost structural integrity.
Water that tastes metallic or has a bluish-green tint coming out of a brass faucet may be picking up copper. First-draw water that smells slightly different from flushed water is another flag. None of these signs constitute an emergency on their own, but they are worth investigating, especially in homes with soft water, older leaded-brass fixtures, or mixed-metal plumbing where galvanic couples might be at work.