Chloramine is a disinfectant made by combining chlorine with ammonia, and it is used by roughly a quarter of large water systems in the United States to keep drinking water free of harmful bacteria as it travels through pipes to your tap. For the general population drinking it at the concentrations found in treated tap water, chloramine is considered safe by the EPA and poses no known health risks. But “safe for most people” and “safe for everyone in every situation” are different statements, and the gap between them is where the interesting questions live. Chloramine interacts differently with pipes, aquariums, medical equipment, and certain byproducts than free chlorine does, and those differences matter in specific ways worth understanding.
How Chloramine Differs From Free Chlorine
Most water treatment plants disinfect water with chlorine. Some then add a controlled amount of ammonia so the chlorine bonds with it, forming monochloramine. This is the dominant form of chloramine in drinking water and the one utilities intentionally produce. It is more stable than free chlorine, meaning it lasts longer as water moves through miles of distribution pipes before reaching homes. Free chlorine tends to dissipate quickly, which can leave the far ends of a water system with little residual disinfectant. Chloramine solves that problem by hanging around longer.
That persistence is the main reason utilities switched. It is not about chloramine being a “stronger” disinfectant. In fact, free chlorine is generally more potent at killing pathogens on contact. The trade-off is that chloramine provides more consistent protection across an entire distribution network, reducing the chance that bacteria regrow in pipes far from the treatment plant.
There are actually three inorganic chloramines: monochloramine, dichloramine, and trichloramine. Monochloramine is the one intentionally produced for drinking water and is soluble and stable. Dichloramine is unstable in water and not deliberately used. Trichloramine does not dissolve well in water at all and tends to evaporate into the air, which is why it becomes a concern in enclosed spaces like indoor swimming pools rather than in tap water.
What the Safety Evidence Says for Drinking
Controlled studies in healthy volunteers have found no clinical effects from drinking water containing monochloramine at the doses typically encountered in treated tap water. In one set of trials, volunteers drank monochloramine-treated water for up to twelve weeks with no observable health effects at doses of about 0.034 mg per kilogram of body weight per day.1Taylor & Francis Online (Crit Rev Toxicol). Inorganic chloramines: a critical review of the toxicological and epidemiological evidence as a basis for occupational exposure limit setting The EPA sets a maximum residual disinfectant level for chloramine in drinking water at 4 mg/L as an annual average, and most utilities keep concentrations well below that.
So if you are a healthy person drinking tap water, the evidence does not point to any meaningful risk from chloramine at regulated levels. The safety picture gets more complicated, though, when you look at specific populations, specific byproducts, and specific infrastructure.
Disinfection Byproducts and the Trade-Off With Chlorine
One of the original motivations for switching to chloramine was to reduce certain disinfection byproducts. When free chlorine reacts with naturally occurring organic matter in water, it can form compounds called trihalomethanes and haloacetic acids. These are regulated because long-term exposure at high levels has been linked to increased cancer risk. Chloramine produces far lower levels of these particular compounds, which is a genuine advantage.
But chloramine creates its own set of byproducts. The one that draws the most research attention is N-nitrosodimethylamine, or NDMA, a probable carcinogen. NDMA forms when monochloramine reacts with certain nitrogen-containing organic compounds in water. Recent research has shown that even dissolved organic matter released from nitrogen-containing microplastics can serve as a precursor for NDMA and related N-nitrosamines during chloramine disinfection.2PubMed. Formation mechanisms of carcinogenic N-nitrosamines from dissolved organic matter derived from nitrogen-containing microplastics during chloramine disinfection This means the byproduct profile can shift depending on what else is in the water, including contaminants that were not a concern decades ago when chloramine protocols were first designed.
The net result is not a clear winner. Chloramine reduces some harmful byproducts and introduces others. Utilities and regulators weigh this trade-off based on the specific characteristics of their water source, their pipe infrastructure, and the distance water has to travel. For the average person, the byproduct levels from either disinfection method are kept within regulated limits. But the idea that chloramine is simply “cleaner” than chlorine oversimplifies the chemistry.
The Lead Problem in Older Pipes
The most serious infrastructure issue tied to chloramine involves lead. This became painfully visible in Washington, D.C., in the early 2000s, when the city switched from free chlorine to chloramine disinfection and lead levels in drinking water spiked dramatically. The cause was a chemical reaction, or rather the absence of one. Free chlorine reacts with dissolved lead to form a protective mineral layer on the inside of lead pipes and lead solder joints. This coating, primarily lead dioxide, is highly insoluble and acts as a barrier preventing lead from leaching into the water. Chloramine does not produce this same protective layer.3Journal AWWA. role of chlorine and chloramine in corrosion of lead‐bearing plumbing materials
Without that barrier, lead dissolved more freely into the water. In Washington, D.C., the highest lead concentrations sometimes appeared after about a minute of flushing, which was particularly troubling because public health guidance at the time told residents to flush their taps for about a minute before drinking to reduce lead exposure.3Journal AWWA. role of chlorine and chloramine in corrosion of lead‐bearing plumbing materials The standard advice was actually making the problem worse.
An analysis of the broader relationship between chloramine use and blood lead levels found that switching to chloramine disinfection could increase blood lead levels in populations served by older housing with lead plumbing, though the effect was progressively reduced in newer homes.4PubMed Central. Changes in blood lead levels associated with use of chloramines in water treatment systems This means that whether chloramine poses a lead risk depends heavily on the age and materials of your plumbing. If your home was built after lead pipes and lead solder were banned in the late 1980s, the concern is much smaller. If you live in an older home, especially one that has never had its service line replaced, the interaction between chloramine and lead is worth knowing about.
Laboratory testing confirmed the mechanism: for desalinated and blended finished waters, more total lead was released in the presence of chloramine than in the presence of free chlorine. For finished groundwater and surface water, however, the difference was not statistically significant.5Journal AWWA. Effect of free chlorine and chloramines on lead release in a distribution system So the type of source water also matters. The takeaway is that chloramine is not universally worse for lead corrosion, but it removes a protective chemical mechanism that free chlorine provides in certain pipe materials, and that removal can have serious consequences.
Why Chloramine Is Dangerous for Dialysis Patients
If there is one group for whom chloramine in water is genuinely dangerous, it is people undergoing hemodialysis. During dialysis, large volumes of water come into direct contact with blood across a membrane. Any chloramine in that water crosses into the bloodstream, where it damages red blood cells and causes hemolytic anemia, a condition where red blood cells break apart faster than the body can replace them.6Nephrology Dialysis Transplantation. Chloramine, a sneaky contaminant of dialysate
This is not a theoretical concern. Documented incidents have resulted in dozens of patients requiring blood transfusions after chloramine-contaminated dialysate entered their systems. In one reported episode, 41 patients needed transfusions to treat hemolytic anemia caused by chloramine exposure during dialysis. While the mortality rate among the affected patients increased in the months following exposure compared to the year before, no individual deaths were directly attributed to that specific incident.7PubMed. Illness in hemodialysis patients after exposure to chloramine contaminated dialysate In addition to hemolytic anemia, chloramine exposure during dialysis has been linked to methemoglobinemia, a condition where the blood’s ability to carry oxygen is impaired.8PubMed. Chloramine-induced methemoglobinemia in a hemodialysis patient
Dialysis centers are required to use carbon filtration systems to strip chloramine from water before it is used, and these systems must be carefully maintained. The danger arises when filters fail, when a utility switches to chloramine without adequate notice, or when home dialysis patients are unaware that their water supply contains chloramine. If you or someone in your household is on dialysis, knowing whether your water utility uses chloramine is critically important, and you should ensure that the filtration equipment is rated to remove it and tested regularly.
Biofilm and Pathogen Control in Building Plumbing
Inside the pipes of large buildings like hospitals, hotels, and apartment complexes, bacteria can form biofilms: thin, sticky colonies that cling to pipe walls and are difficult to kill. One pathogen of particular concern is Legionella pneumophila, the bacterium that causes Legionnaires’ disease. How well chloramine controls Legionella compared to free chlorine depends on what the pipes are made of.
Research on Legionella in simulated building water systems found that the effectiveness of each disinfectant varied with the pipe material. Monochloramine was more effective at reducing Legionella in copper pipe biofilms, while free chlorine was more effective in PVC pipe biofilms. For free-floating bacteria not embedded in biofilm, free chlorine was more effective overall.9PubMed Central. Chlorine and Monochloramine Disinfection of Legionella pneumophila Colonizing Copper and Polyvinyl Chloride Drinking Water Biofilms This means there is no universal answer to whether chloramine or chlorine is “better” at pathogen control in building plumbing. The answer depends on the specific plumbing materials and the form the bacteria take.
For building managers dealing with Legionella prevention, this is a practical consideration. A chloraminated water supply can offer good biofilm control in copper systems but may be less effective in plastic plumbing, which is increasingly common in modern construction. Supplemental disinfection strategies are often needed regardless of what the municipal utility provides.
Nitrification in the Distribution System
Chloramine introduces a complication in water distribution that free chlorine does not: nitrification. Because chloramine is made from chlorine and ammonia, its gradual breakdown in pipes releases small amounts of free ammonia. This ammonia becomes food for nitrifying bacteria that naturally inhabit the pipe system. These bacteria convert ammonia to nitrite and then to nitrate, and their growth can accelerate chloramine decay, creating a feedback loop.10PubMed Central. Microbial Nitrogen Metabolism in Chloraminated Drinking Water Reservoirs
The result can be a drop in disinfectant residual and a rise in nitrite levels, both of which are problems. Utilities that use chloramine have to actively monitor for nitrification, especially in warmer months when bacterial activity increases. When nitrification takes hold in a section of the system, the standard fix is a “chlorine burn,” which is a temporary switch from chloramine back to free chlorine to knock the nitrifying bacteria back down.11PubMed. The “Burn”: water quality and microbiological impacts related to limited free chlorine disinfection periods in a chloramine system If your utility issues a notice about a temporary switch to chlorine disinfection, nitrification control is usually the reason.
These chlorine burns are effective at suppressing nitrification in the short term, though research describes their effect as transient rather than permanent.12PubMed Central. Reconsider the burn: The transient effect of a chlorine burn on controlling opportunistic pathogens in a full-scale chloraminated engineered water system Nitrification tends to come back after the system returns to chloramine, meaning utilities often need to repeat the process periodically. For consumers, the practical implication is minor, but you may notice a temporary change in how your water smells or tastes during these periods.
Taste, Smell, and the Swimming Pool Connection
Many people associate the harsh chemical smell of indoor swimming pools with “chlorine,” but that smell actually comes primarily from trichloramine, the third and most volatile form of chloramine. Trichloramine forms when chlorine reacts with nitrogen compounds introduced by swimmers (sweat, urine, skin oils). It does not dissolve well in water and instead escapes into the air, which is why indoor pools with poor ventilation can feel harsh on the eyes and throat. Occupational studies have found exposure-response relationships between airborne trichloramine levels and irritation of the eyes and upper airways in indoor pool workers.1Taylor & Francis Online (Crit Rev Toxicol). Inorganic chloramines: a critical review of the toxicological and epidemiological evidence as a basis for occupational exposure limit setting
This is chemically distinct from what happens in your tap water. Municipal chloramination produces monochloramine, which is stable and stays dissolved. Trichloramine forms under completely different conditions and concentrations than those found in treated drinking water. So the swimming pool analogy, which is often the reason people worry about chloramine in their tap water, does not really apply.
As for the taste and smell of monochloramine in drinking water, research has explored the flavor thresholds. One study using trained taste panels attempted to determine at what concentration people could detect chloramine flavor in water, but found that the results were difficult to pin down precisely because of outlier responses in the low-concentration range where municipal water typically sits.13PubMed Central. Characteristics of salt taste and free chlorine or chloramine in drinking water In practice, some people report a rubbery or medicinal taste in chloraminated water, and complaints tend to increase when chloramine residuals are on the higher end. Unlike chlorine, which dissipates quickly if you leave a glass of water sitting out, chloramine does not off-gas easily. Filling a pitcher and waiting an hour, a common trick for chlorine-tasting water, will not help with chloramine. A carbon filter is a more effective solution for taste and odor.
What Chloramine Means for Fish Tanks and Home Brewing
Two groups that feel the effects of chloramine acutely are aquarium hobbyists and home brewers. Chloramine is toxic to fish because it passes through their gills and damages red blood cells in much the same way it damages blood cells in dialysis patients. And because chloramine does not evaporate from water the way free chlorine does, the old aquarium advice of letting water sit out for 24 hours before adding it to a tank does not work. You need a water conditioner specifically designed to neutralize chloramine, or a carbon filter rated for the purpose.
Home brewers face a similar issue. Chloramine can react with compounds in beer and produce chlorophenols, which create a medicinal or band-aid-like off-flavor. Again, the standard homebrew advice of boiling water to drive off chlorine does not reliably remove chloramine. A campden tablet (potassium metabisulfite) added to the brewing water before use is the common fix, as it breaks the chloramine bond almost instantly.
Removing Chloramine at Home
If you want to reduce or eliminate chloramine from your water for any reason, the key fact is that standard methods for removing chlorine often do not work. Boiling is ineffective for practical purposes. Letting water sit out does almost nothing. Reverse osmosis systems will remove it, but they are more expensive and slower than simple filtration. The most accessible option is a catalytic activated carbon filter, which breaks the chloramine bond and adsorbs both the chlorine and ammonia components. Standard granular activated carbon filters work, but much more slowly and with less capacity than catalytic carbon, so if your primary concern is chloramine rather than just chlorine, look for filters that specifically state they are rated for chloramine removal.
Whole-house filtration systems are available for people who want chloramine removed from every tap, including showers. Some people with sensitive skin or conditions like eczema report that chloraminated water aggravates their symptoms, though clinical evidence on this is limited. Whether the cost of whole-house filtration is justified depends on your specific situation, including whether you have lead plumbing that might benefit from a different water chemistry, fish tanks that need safe water, or household members on dialysis equipment.
For most people, a countertop or under-sink carbon filter addresses the taste issue without any larger intervention. The important thing is checking that the filter’s certification covers chloramine, not just chlorine, since many inexpensive pitcher filters handle chlorine well but barely touch chloramine.