Chloramine and Chlorine in Drinking Water

What Are Chloramine and Chlorine?

Chlorine and chloramine are chemical disinfectants that water utilities add to drinking water to kill bacteria, viruses, and other pathogens. They are the reason tap water in the United States is generally safe from waterborne diseases like cholera and typhoid — a public health achievement that dates back over a century.

Chlorine has been used in US water treatment since 1908 and remains the most common disinfectant nationwide. A growing number of systems have shifted to chloramine, which is formed by combining chlorine with ammonia. More than 20% of US water systems, serving roughly 68 million people, now use chloramine as their primary or secondary disinfectant.

The key difference between the two is persistence. Chlorine dissipates relatively quickly and evaporates from an open glass of water within a matter of hours. Chloramine is far more stable, lasting longer as it travels through distribution pipes — sometimes for days. That stability is precisely why utilities favor it for residual disinfection across large, sprawling systems. But the same stability that makes chloramine attractive to utilities also makes it harder to remove at the point of use and means it lingers throughout household plumbing in ways that chlorine does not.

How They Get Into Drinking Water

Chlorine and chloramine are intentionally added during water treatment. The EPA requires all public water systems using surface water to maintain a detectable disinfectant residual throughout the distribution system, from the treatment plant all the way to the consumer’s tap.

Chlorine is added as chlorine gas, sodium hypochlorite (liquid bleach), or calcium hypochlorite (a dry form). Utilities choose the form based on system size, cost, and safety logistics. Chloramine is produced on-site by adding ammonia to chlorinated water in controlled ratios — typically 3:1 to 5:1 chlorine-to-ammonia by weight — a process that takes place within the treatment facility before water enters the distribution system.

The shift toward chloramine accelerated after the EPA tightened rules on disinfection byproducts (DBPs). When chlorine reacts with naturally occurring organic matter in source water, it forms trihalomethanes (THMs) and haloacetic acids (HAAs), both regulated as probable human carcinogens. Because chloramine is less reactive with organic matter, utilities that were struggling to meet THM and HAA limits often switched to chloramine as a compliance strategy.

The trade-off is that chloramine creates its own class of byproducts. Reactions between chloramine and organic nitrogen compounds can produce nitrosamines, most notably N-nitrosodimethylamine (NDMA). NDMA is a potent animal carcinogen and is under active regulatory scrutiny. This means chloramine does not eliminate the DBP problem — it reshapes it.

Health Effects

At the levels maintained in public drinking water, chlorine and chloramine are not considered acutely toxic. The EPA and public health agencies broadly agree that the benefits of disinfection — preventing waterborne disease outbreaks — far outweigh the risks associated with residual disinfectants. Nevertheless, several health concerns are well documented.

Taste and Odor

Taste and odor are the most common complaints associated with disinfectants. Chlorine gives water a recognizable swimming-pool taste and smell that many people find unpleasant, particularly at the higher end of the allowed range. Chloramine produces a more muted but persistent chemical or rubbery taste that can be equally objectionable. Because chloramine is more stable, the off-taste does not dissipate when water sits in a pitcher or glass — unlike chlorine, it requires active filtration to remove.

Skin and Respiratory Irritation

Both disinfectants can aggravate existing skin conditions, including eczema, psoriasis, and contact dermatitis. This effect is most notable during bathing and showering, when skin is exposed to water for extended periods. Showering in chlorinated water also releases volatile chlorine compounds into the bathroom air, which can irritate the respiratory tract. People with asthma or other respiratory sensitivities often report worsening symptoms in heavily chlorinated water supplies. Chloramine is less volatile than chlorine, so inhalation risk during showering is somewhat lower, though skin contact effects remain.

Disinfection Byproducts

While DBPs are not caused by the disinfectants themselves, they are a direct consequence of using chlorine or chloramine to treat water containing organic matter. Long-term exposure to trihalomethanes and haloacetic acids has been associated with increased risk of bladder cancer, as well as adverse reproductive outcomes including low birth weight and increased miscarriage risk. Chloramine-based systems that produce NDMA face additional scrutiny, as NDMA is classified as a probable human carcinogen. See the full disinfection byproducts guide for a detailed breakdown.

Lead Leaching Risk

One of the most serious and underappreciated risks associated with chloramine is its potential to accelerate lead release from aging pipe infrastructure. This concern is not theoretical — it was demonstrated catastrophically in Washington, DC.

From 2000 to 2004, the DC Water and Sewer Authority switched from chlorine to chloramine as its primary disinfectant, driven by the same DBP compliance pressures that motivated utilities across the country. What the switch inadvertently did was destabilize the protective mineral scale — primarily lead carbonate and calcium carbonate — that had built up on the interior surfaces of the city’s thousands of lead service lines over decades. Chloramine altered the water’s oxidation-reduction chemistry in ways that chlorine did not, stripping away that protective coating and exposing the underlying lead pipe material directly to drinking water.

The result was a sharp increase in lead concentrations at the tap. A 2004 Washington Post investigation and subsequent peer-reviewed research found that blood lead levels in children under the age of two in DC rose measurably during this period. A study published in Environmental Science and Technology estimated that between 42,000 and 85,000 children were exposed to water exceeding the EPA action level of 15 parts per billion during the years of the crisis. The situation was compounded by a slow public health response and inadequate monitoring that failed to catch the problem early.

The DC crisis did not establish that chloramine is inherently dangerous — it established that switching disinfectants in a system with aging lead infrastructure requires careful chemical assessment and immediate enhanced monitoring. The event became a case study in how disinfectant decisions have downstream consequences that extend well beyond DBP compliance. For households with older plumbing, lead service lines, or brass fixtures, knowing whether your system uses chloramine — and whether it has recently switched — is directly relevant to lead exposure risk. See the lead contamination guide and copper guide for more on corrosion-related risks.

Special Populations

Three groups face heightened risks that go beyond the general population:

• Dialysis patients: Chloramine must be completely removed from water used in hemodialysis machines. Even trace amounts that are entirely safe for drinking can pass directly into a patient’s bloodstream through the dialysis membrane and cause hemolytic anemia — a potentially fatal breakdown of red blood cells. Dialysis centers use specialized filtration to address this, but home dialysis patients must be particularly vigilant.
• Fish, amphibians, and reptiles: Chloramine is toxic to aquatic animals at concentrations that are safe for human consumption. Unlike chlorine, which off-gasses from a fish tank if water is left to sit, chloramine does not evaporate. Aquarium and pond owners must use dechloraminators — sodium thiosulfate alone is insufficient — and should always verify which disinfectant their utility uses before water changes.
• Homebrewers: Chloramine reacts with phenolic compounds during brewing to produce chlorophenols, which create harsh medicinal or plastic off-flavors even at very low concentrations. Campden tablets (potassium metabisulfite) or catalytic carbon filtration are standard treatments for chloraminated water in brewing applications.

EPA Regulation and Limits

The EPA regulates chlorine and chloramine as Maximum Residual Disinfectant Levels (MRDLs), a regulatory category distinct from contaminant limits. MRDLs reflect the fact that these chemicals are added intentionally and that some level of residual is required for public health protection.

Disinfectant	MRDL	MRDLG (Goal)
Chloramine	4.0 mg/L (as Cl₂)	4.0 mg/L
Chlorine	4.0 mg/L	4.0 mg/L
Chlorine dioxide	0.8 mg/L	0.8 mg/L

In practice, most systems maintain 0.5 to 2.0 mg/L for free chlorine and 1.0 to 4.0 mg/L for chloramine. Operating toward the lower end of these ranges improves taste and reduces DBP formation but can risk inadequate residual at the distant ends of large distribution systems. The EPA also sets maximum limits for disinfection byproducts: THMs at 80 µg/L and HAAs at 60 µg/L as running annual averages.

MRDL violations occur when a utility’s quarterly average exceeds the limit. These are relatively uncommon — most utilities manage their disinfectant levels carefully — but they do occur and are publicly reported.

How Widespread Are Chloramine and Chlorine?

Chlorine remains the dominant disinfectant in the United States by number of systems, but chloramine serves a disproportionately large share of the population because its adoption has been concentrated among large metropolitan utilities. More than 20% of US water systems now use chloramine as their primary disinfectant, and those systems collectively serve approximately 68 million Americans — roughly one in five people on a public water supply.

The trend toward chloramine adoption has continued to grow, particularly among mid-size to large utilities facing tightening DBP limits under the Stage 1 and Stage 2 Disinfectants and Disinfection Byproducts Rules. Cities that switched to chloramine in recent decades include Philadelphia, San Francisco, Houston, Denver, and Washington, DC (post-crisis, with enhanced corrosion control). Many smaller systems in rural areas continue to use chlorine because their distribution systems are shorter, making residual maintenance easier.

The geographic distribution is uneven. Systems drawing from surface water — rivers, lakes, and reservoirs — are more likely to have high natural organic matter content, which drives DBP formation and pushes utilities toward chloramine. Groundwater-based systems often have lower organic matter and may find chlorine adequate. In practice, a utility’s disinfectant choice is shaped by source water chemistry, infrastructure age, system size, and regulatory compliance history.

Because the shift from chlorine to chloramine affects filtration needs, lead exposure risk, and the safety of water for special uses, knowing which disinfectant your system uses is foundational to understanding your tap water.

How WaterVerge Tracks Disinfectants

WaterVerge uses data from the EPA’s Safe Drinking Water Information System (SDWIS) to monitor disinfectant levels and associated violations across thousands of water systems nationwide. We track MRDL violations for chlorine, chloramine, and chlorine dioxide, as well as violations for disinfection byproducts — THMs and HAAs — which are the regulatory consequence of disinfection chemistry.

Each city profile on WaterVerge shows which disinfectant your utility uses, the most recently reported residual levels, and whether any MRDL or DBP violations have occurred in the past five years. We also flag systems that have recently switched from chlorine to chloramine, since that transition can catch residents off guard. Aquarium owners, dialysis patients relying on home equipment, and homebrewers all need advance notice to adjust their water treatment accordingly. Lead exposure risk associated with a switch is also noted where relevant infrastructure data is available.

How to Remove Chloramine and Chlorine

The right removal method depends critically on which disinfectant your system uses. This distinction matters because the two chemicals respond differently to common filtration technologies. Using a filter designed for chlorine in a chloraminated system provides a false sense of protection.

For chlorine removal:

• Granular activated carbon (GAC): Effective and widely available. Most pitcher filters, faucet-mount filters, and refrigerator filters use GAC and reduce chlorine effectively. NSF/ANSI Standard 42 certification confirms chlorine taste and odor reduction.
• Letting water sit: Chlorine dissipates from an open, uncovered container within 24 hours. Practical for filling a fish tank or watering plants, but not a reliable solution for daily drinking water.

For chloramine removal:

• Catalytic carbon: A specially treated form of activated carbon engineered to break the chloramine bond through catalytic reduction, not just adsorption. Standard activated carbon has very limited effectiveness against chloramine. Whole-house catalytic carbon systems provide the most comprehensive coverage and are available from multiple manufacturers.
• Reverse osmosis (RO): Under-sink RO systems with a catalytic or activated carbon pre-filter reduce chloramine by 95% or more, along with many byproducts. The carbon pre-filter protects the RO membrane, which can be degraded by chloramine exposure.
• Vitamin C (ascorbic acid) filters: Neutralize both chlorine and chloramine on contact through a chemical reduction reaction. Commonly used in shower filters as a practical solution for people with skin sensitivity, since whole-house carbon systems can be costly.

Filter comparison:

Method	Chlorine Removal	Chloramine Removal	Certification	Best For
Standard GAC pitcher filter	High	Low	NSF/ANSI 42	Chlorine-only systems
Catalytic carbon (whole house)	High	High	NSF/ANSI 42	Chloramine systems, all uses
Under-sink RO + carbon pre-filter	High	High	NSF/ANSI 58	Chloramine + byproducts
Vitamin C shower filter	High	High	—	Bathing, skin sensitivity
Sitting in open container	High	None	—	Plants, fish tanks (chlorine only)

When selecting a filter, confirm whether your utility uses chlorine or chloramine first — your WaterVerge city profile will show this. See our guide to the best water filter pitchers for specific product recommendations sorted by disinfectant type.

Check Your City

Disinfectant type and residual levels vary significantly between water systems. A large city using chloramine at 3.5 mg/L presents different filtration needs and different secondary risks than a small rural system using chlorine at 0.8 mg/L — and the right filter depends entirely on knowing which disinfectant is in your water.

Search your city on WaterVerge to find out which disinfectant your utility uses, view recent residual levels, and check for any MRDL or disinfection byproduct violations. If your system has recently switched from chlorine to chloramine, that transition will be flagged in your city profile along with guidance on what the change means for filtration, lead exposure risk, aquariums, and other special uses.