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Chloramine vs Chlorine in Tap Water: A 2026 Guide

Two disinfectants account for nearly all microbial control in US municipal drinking water: free chlorine and chloramine. They are chemically related — chloramine is produced by combining chlorine with ammonia — but they behave differently inside a treatment plant, inside a distribution pipe, and inside a household filter. According to the EPA’s most recent occurrence data, roughly one in five Americans (about 68 million people) receives water disinfected primarily with chloramine. The remainder receives free chlorine, with a smaller fraction served by alternative methods like ozone or chlorine dioxide that still rely on a chlorine or chloramine residual in the distribution system.

The distinction matters. The disinfectant in your tap water determines what its byproducts look like, what odors and tastes you may notice, and whether a standard activated carbon pitcher filter will reliably remove it. Here is what the data actually shows.

What Is Chlorine in Drinking Water?

Chlorine has been used to disinfect US drinking water since 1908, when Jersey City became the first municipality to chlorinate its supply. In water, elemental chlorine (Cl₂) reacts with H₂O to form hypochlorous acid (HOCl) and hypochlorite ion (OCl⁻). Collectively, these species are referred to as “free chlorine,” and they are what most utilities measure when reporting chlorine residual.

Free chlorine is a strong oxidant. It inactivates bacteria, most viruses, and the protozoan parasite Giardia by oxidizing cellular components. It does not consistently inactivate Cryptosporidium at standard contact times — a known regulatory limitation addressed through additional treatment barriers such as filtration and UV.

Typical chlorine residuals in US distribution systems range from 0.2 to 4.0 mg/L. The EPA’s maximum residual disinfectant level (MRDL) caps chlorine at 4.0 mg/L as a running annual average. Free chlorine dissipates relatively quickly in water — residual can fall by half within hours in the absence of additional dosing or in the presence of organic matter. That instability is one reason many large utilities switched to chloramine for distribution.

What Is Chloramine in Drinking Water?

Chloramine — more specifically monochloramine (NH₂Cl) — is formed when ammonia is added to chlorinated water in a controlled ratio (typically around 4 parts chlorine to 1 part ammonia by weight). The reaction produces a more stable but weaker disinfectant than free chlorine.

Two other chloramine species can form under different pH and ratio conditions: dichloramine (NHCl₂) and trichloramine (NCl₃, also called nitrogen trichloride). Monochloramine is the intended product. Dichloramine and trichloramine are associated with the chlorine-pool odor familiar from indoor swimming facilities and are generally considered undesirable in finished drinking water.

Chloramine persists in distribution pipes far longer than free chlorine. That stability is its main operational advantage: in older urban water systems with thousands of miles of pipe, chloramine maintains a disinfectant residual all the way to the customer’s tap. Adoption is concentrated in large utilities, including those serving Washington D.C., Philadelphia, San Francisco, Tampa, and most of the Texas Gulf Coast.

Why Utilities Switched from Chlorine to Chloramine

The shift to chloramine in many large US systems was not arbitrary. It traces to the Stage 1 and Stage 2 Disinfectants and Disinfection Byproducts Rules (D/DBPR), promulgated by the EPA in 1998 and 2006. These rules tightened the maximum contaminant levels for total trihalomethanes (TTHM, set at 80 µg/L) and five haloacetic acids (HAA5, set at 60 µg/L) as locational running annual averages.

Free chlorine reacts with naturally occurring organic matter — primarily decayed plant material in source water — to form THMs and HAAs. These compounds are classified as probable human carcinogens, with epidemiological associations to bladder cancer and adverse reproductive outcomes. Chloramine, being a weaker oxidant, produces substantially fewer THMs and HAAs than free chlorine at equivalent contact times.

That claim requires context. Chloramine reduces the formation of regulated DBPs, but it produces a different set of byproducts that have raised separate concerns:

N-Nitrosodimethylamine (NDMA): A nitrogenous DBP classified by the EPA as a probable human carcinogen. NDMA is not currently regulated under the Safe Drinking Water Act, but it appears on the EPA’s Contaminant Candidate List 5 and is monitored under several states’ notification levels. California, for example, sets a public health notification level of 10 ng/L.
Iodinated DBPs: Including iodoacetic acid, which in vitro toxicology studies suggest may be more cytotoxic than its chlorinated counterparts.
Cyanogen chloride: A nitrogenous DBP that forms at low levels in chloraminated water.

The regulatory framework reflects an explicit trade. The EPA accepted higher levels of these unregulated nitrogenous DBPs in exchange for measurable reductions in the regulated THM and HAA5 levels. Independent researchers, including authors of a 2018 review in Environmental Science & Technology, have noted that the net public health impact of that trade is not fully resolved.

Health Effects: Chlorine vs Chloramine

At residual concentrations within the EPA’s MRDL of 4.0 mg/L, neither free chlorine nor chloramine is acutely toxic to most people through ingestion. The CDC and World Health Organization both classify these residuals as posing minimal direct health risk in finished drinking water.

The relevant health questions involve indirect or population-specific effects:

Sensitive populations. Chloramine is acutely toxic to fish, reptiles, and amphibians, which absorb the disinfectant directly across their gills or skin. Hemodialysis patients are also at risk: chloramine in dialysate water can cross the dialyzer membrane and cause hemolytic anemia. Dialysis clinics in chloraminated service areas are required to use additional carbon filtration and, in some protocols, ascorbic acid pretreatment.
Respiratory and skin effects. Some individuals report eye and skin irritation, eczema flares, and respiratory symptoms in chloraminated water. The mechanistic evidence is mixed; a 2010 review in Annals of Allergy, Asthma & Immunology found suggestive but inconclusive associations between disinfection byproducts and respiratory outcomes.
Cancer risk from DBPs. Both disinfectants produce DBPs associated with elevated bladder cancer risk in pooled epidemiological studies. Current consensus is that the risk from DBPs is real but small at typical exposure levels, and is considered smaller than the disease risk from drinking inadequately disinfected water.

For broader context on what is and is not regulated in US tap water, see our overview of tap water safety in the US.

Taste, Smell, and Physical Signs

Free chlorine has a sharp, distinctive odor that most people can detect at concentrations above approximately 0.3 mg/L. The smell tends to dissipate when water is left in an open container — chlorine off-gasses into the atmosphere within a few hours.

Chloramine has a milder odor and is far less volatile. Leaving chloraminated water on the counter does not noticeably reduce the residual. A faint chemical or “pool” smell may be present, particularly if dichloramine has formed during distribution.

Two practical implications follow. First, if your water smelled like chlorine years ago but now has a milder, more persistent odor, your utility likely transitioned to chloramine. Second, off-gassing as a removal method works only for free chlorine. It does not work for chloramine.

How to Find Out Which Disinfectant Your Utility Uses

The most direct source is your annual Consumer Confidence Report (CCR), which every community water system is required to publish by July 1 each year. The CCR will list the disinfectant residual under headings such as “Chlorine” or “Chloramine (as Cl₂).” If your utility uses chloramine, the CCR will also report ammonia levels.

For independent verification, see our guide on how to test your water at home. A standard total chlorine test strip will detect both free chlorine and chloramine. A free chlorine test strip will detect only chlorine. If total chlorine reads positive but free chlorine is near zero, chloramine is present.

Removing Chlorine from Tap Water

Free chlorine is among the easiest contaminants to remove. Standard granular activated carbon (GAC) and carbon block filters reduce chlorine effectively through adsorption — the carbon’s high internal surface area binds chlorine species out of solution.

Pitcher-style filters, faucet-mount filters, and refrigerator filters that hold NSF/ANSI 42 certification for chlorine taste and odor reduction will measurably lower free chlorine, generally to levels below human detection. NSF 42 is the relevant standard because chlorine is classified as an aesthetic concern, not a health-based MCL contaminant. The distinction matters: a filter certified for NSF 42 chlorine reduction is doing the job the standard was designed to do.

For under-sink and whole-house systems, our under-sink filter buying guide and whole-house filter buying guide cover certified options at multiple price points. For lower-volume needs, pitcher filters handle chlorine well.

Removing Chloramine: Harder Than Chlorine

This is where the chemistry diverges from common assumptions. Standard granular activated carbon — the kind in most basic pitcher filters and entry-level under-sink cartridges — does reduce chloramine, but slowly and inconsistently. The reaction between chloramine and carbon is kinetically limited, and short contact times in a pitcher or low-flow cartridge do not allow chloramine to be reliably removed.

The two methods that work consistently for chloramine are:

Catalytic activated carbon. Catalytic carbon is a thermally modified form of activated carbon with enhanced surface chemistry that accelerates the reaction between chloramine and the carbon, converting chloramine into chloride, nitrogen gas, and ammonia. Whole-house systems including the SpringWell CF and the Aquasana Rhino series specify catalytic carbon for this reason. NSF certification for chloramine reduction under NSF/ANSI 42 requires the filter to demonstrate sustained reduction over a defined service life — not every carbon filter on the market meets that requirement.
Reverse osmosis (with carbon prefilter). A well-designed RO system pairs a carbon prefilter (which handles most of the chloramine and protects the downstream membrane) with a thin-film composite membrane that further reduces nitrogenous compounds. RO systems certified to NSF/ANSI 58 for health-effects contaminants are typically also certified to NSF/ANSI 42 for chlorine and chloramine taste and odor reduction.

A common mistake is assuming that a pitcher filter rated for chlorine will perform identically on chloramine. It will not. If your utility uses chloramine and your goal is consistent reduction, the most reliable approach is point-of-entry catalytic carbon or point-of-use reverse osmosis.

When installing under-sink or whole-house filtration, use compression fittings rather than saddle valves. A growing number of municipalities now restrict saddle valves in plumbing codes due to long-term leak risk, and compression fittings are the durable standard for both rented and owned homes.

NSF Certifications to Look For

Filter certification for chlorine and chloramine reduction falls under NSF/ANSI 42, the standard for aesthetic effects. Within NSF 42, certifications can include:

Chlorine reduction (Class I or Class II): Class I requires at least 75% reduction at higher influent concentrations. Class II requires at least 50% reduction.
Chloramine reduction: A separate test protocol within NSF 42 that requires sustained reduction over the manufacturer’s stated cartridge capacity.

For verification, the NSF Certified Drinking Water Treatment Units database lists every certified product along with the specific contaminants tested. The phrase “tested to NSF standards” in marketing copy is not equivalent to NSF certification. “Tested to” language indicates third-party laboratory verification at a single point in time. NSF certification involves ongoing factory audits, annual re-testing, and unannounced inspections. Both are legitimate forms of verification — but only one is monitored continuously.

NSF P473, the legacy protocol for PFAS reduction, was incorporated into NSF 53 in 2019. It is not a separate current standard. If a filter advertises “NSF P473 certified” today, that certification has been absorbed under NSF 53 and is verifiable in the same database. The certification frameworks for chloramine and PFAS are different — a filter listed under NSF 42 for chloramine reduction tells you nothing about its PFAS performance, and vice versa.

Key Takeaways

Free chlorine and chloramine are both EPA-approved disinfectants. Chloramine serves roughly 68 million Americans, primarily through large urban water systems.
Chloramine was adopted to reduce regulated disinfection byproducts (THMs and HAA5) but produces a different set of byproducts including NDMA, some of which remain unregulated.
At residual levels within the EPA’s 4.0 mg/L MRDL, neither disinfectant poses acute health risks to most adults through ingestion. Hemodialysis patients, fish, and reptiles require additional protection from chloramine.
Free chlorine is straightforward to remove with standard activated carbon. Chloramine requires catalytic carbon or reverse osmosis for reliable reduction.
NSF/ANSI 42 is the relevant certification for both contaminants — but chloramine reduction is a separate test within that standard. Verify the specific certification in the NSF database before purchasing.

Frequently Asked Questions

Q: How can I tell if my tap water has chlorine or chloramine? Check your annual Consumer Confidence Report, which every public water system publishes by July 1. The disinfectant used will be listed by name. For independent verification, use a total chlorine test strip alongside a free chlorine test strip. If total chlorine reads positive but free chlorine is near zero, your utility is using chloramine.

Q: Does boiling water remove chloramine? Not effectively. Boiling free chlorine for 15 to 20 minutes can reduce it substantially through off-gassing. Chloramine is far more stable and does not volatilize readily. Boiling reduces it only slightly and is not a practical removal method. The reliable approaches are catalytic carbon filtration or reverse osmosis.

Q: Is chloramine safe to drink? For most adults, yes — at residual concentrations within the EPA’s MRDL of 4.0 mg/L. The CDC, WHO, and AWWA all consider chloraminated water safe for ingestion at typical residual levels. The recognized exceptions are dialysis patients, fish and reptile keepers, and individuals with documented sensitivity. The longer-term question of nitrogenous disinfection byproducts is an active area of research.

Q: Do Brita filters remove chloramine? Most standard Brita pitcher filters are NSF/ANSI 42 certified for chlorine reduction. They are not certified for chloramine reduction. The Brita Elite (formerly Longlast+) has longer carbon contact time and may reduce some chloramine, but it does not hold NSF certification specifically for chloramine. For consistent chloramine reduction, a catalytic carbon point-of-use or point-of-entry filter is the verified solution.

Q: Why does my water smell more like a swimming pool in summer? Two reasons are common. First, warmer water increases volatility of chlorine compounds, making the odor more noticeable. Second, some utilities raise chlorine or chloramine residuals seasonally to compensate for higher microbial activity in warm distribution lines. If the smell becomes objectionable, an activated carbon pitcher (for chlorine) or a catalytic carbon under-sink filter (for chloramine) will substantially reduce it.

Sources Cited

US Environmental Protection Agency, “Drinking Water Disinfection: Chlorine and Chloramine,” EPA 815-F-09-007.
US EPA, “Stage 2 Disinfectants and Disinfection Byproducts Rule” (Final Rule, 71 FR 388, January 4, 2006).
US EPA, “Contaminant Candidate List 5 — CCL 5,” EPA-OW-2018-0594.
CDC, “Drinking Water Treatment — Chloramines and Drinking Water Disinfection” fact sheet.
World Health Organization, “Guidelines for Drinking-Water Quality, Fourth Edition Incorporating the First Addendum” (2017), chapter on chemical hazards.
NSF International, Certified Drinking Water Treatment Units database.
Krasner, S.W. et al., “Occurrence of a New Generation of Disinfection Byproducts,” Environmental Science & Technology, 40(23):7175–7185 (2006).
Plewa, M.J. et al., “Halonitromethanes, a Subclass of Drinking Water Disinfection Byproducts: Chemical Characterization and Toxicity,” Environmental Science & Technology, 52(15):8203–8211 (2018).
AWWA, “Water Chlorination/Chloramination Practices and Principles,” AWWA Manual M20.

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