Guide

Chloramine — what actually reduces it, and what cannot

Chloramine needs minutes of contact time. A shower filter gives it seconds. Here is the arithmetic, the standards, and why this page sells you nothing.

Start by finding out whether this applies to you

Many US water utilities use chloramine rather than free chlorine as the disinfectant that stays in the pipes on the way to your house. A large minority of the country is on it — published estimates range from more than one in five people to roughly a third of systems, and the figures are not reconcilable because different sources count people and systems differently.

Finding out which you have costs nothing. Community water systems are required by federal rule to publish an annual Consumer Confidence Report, and it names the disinfectant. If you would rather skip the reading, the utility will tell you over the phone.

This matters more than most water questions, because chloramine and free chlorine behave so differently in a filter that equipment which works well for one is close to irrelevant for the other.

What chloramine is, and why your utility uses it

Chloramine is formed by combining chlorine with ammonia. The form used in drinking water is monochloramine.

Utilities did not switch on a whim. Chlorine reacts with organic matter in water to form disinfection byproducts, and two of those groups — trihalomethanes and haloacetic acids — are federally regulated with enforceable limits. Chloramine forms fewer of those regulated byproducts and persists much longer in the distribution system, which is exactly what you want from a disinfectant that has to survive miles of pipe.

That persistence is the whole point, and it is also the problem. A disinfectant designed not to break down easily does not break down easily in your filter either.

There is a genuine trade-off here that regulators acknowledge rather than hide: chloramine reduces the regulated byproducts while having the potential to form other, unregulated ones. That is a treatment decision with real engineering arguments on both sides, and it is managed continuously by people who do this professionally.

Why it is so much harder to remove

Here is the piece almost nobody explains.

Carbon does not remove chlorine or chloramine by adsorption — by soaking it up the way it soaks up organic compounds. It removes both by a chemical reaction at the carbon surface. And that changes what the limiting factor is.

For something adsorbed, the constraint is capacity: how much carbon you have. For chloramine, the constraint is time. The reaction is slow, and no amount of extra media compensates if the water is moving through faster in proportion.

Water treatment has a term for this: empty bed contact time, or EBCT — how long a parcel of water spends inside the media. The published requirements are unusually consistent across sources that have no particular reason to agree with each other:

Those figures come from a trade association, a peer-reviewed dissertation, the carbon manufacturers themselves, and a federal healthcare regulator. Chloramine needs something like five to ten times the contact time free chlorine does. That is about as well corroborated as consumer-relevant water chemistry gets.

The arithmetic, which you can check yourself

The federal statutory maximum for a showerhead is 2.5 gallons per minute — about 9.5 litres a minute. Real showers commonly run somewhere between 1.5 and 2.5.

To hold water in contact with media for four minutes at 2.5 gpm, you need roughly 38 litres of media — about 1.3 cubic feet. That is a tank standing on the floor. For ten minutes you need around 95 litres.

A typical inline shower cartridge holds somewhere between 0.2 and 0.4 litres of media.

At 0.3 litres and 2.5 gpm, the water is in contact with the media for about two seconds. Even at a gentle 1.5 gpm it is a little over three.

Two seconds, against a requirement measured in minutes. The gap is roughly a hundredfold. To close it, the cartridge behind your showerhead would need to be about a hundred times larger.

This is not a criticism of any particular product. It is a statement about volume and flow rate, and it applies to every inline shower filter regardless of what is inside it or what it costs. Physics is doing the limiting here, not manufacturing quality.

What the media actually do

Ordinary activated carbon works, given ten minutes or more. That is achievable in a properly sized tank system. It is not achievable in seconds.

Catalytic carbon is activated carbon whose surface has been modified to speed the reaction up. It genuinely reduces the contact time required, to something like four to seven minutes. It reduces the requirement; it does not remove it. If you see catalytic carbon recommended for chloramine, that recommendation is sound — and it comes with a sizing condition that is usually left off.

KDF is a copper-zinc alloy that works by a redox reaction, and it is genuinely good at free chlorine. On chloramine, the honest position is that the evidence is thin and comes from the manufacturer. The one published study showing high chloramine reduction used a different grade of KDF than the one in shower filters — the study explicitly chose the other grade for this purpose — along with roughly 0.25 cubic feet of media, twenty to twenty-eight seconds of contact, and an unusually low incoming concentration. There is no independent replication, and no published data at all on the shower-filter grade at the concentrations actually found in tap water.

Reverse osmosis membranes do not reliably remove chloramine. It passes through and can damage the membrane, which is why a carbon prefilter is standard practice in every RO system worth buying. When an RO system removes chloramine, the carbon is doing it.

One thing that almost never appears in consumer material: when carbon reacts with chloramine, it releases ammonia into the treated water. That is the chemistry working as expected, not a fault, but it is worth knowing about.

What the certifications cover

This is where a lot of money changes hands on a misunderstanding.

Chloramine reduction is certified under NSF/ANSI 42, the aesthetic-effects standard. It is not covered by 53, the health-effects standard, and not by 401.

Shower filters have their own standard, NSF/ANSI 177 — and this is the important part. It certifies reduction of free available chlorine. Not chloramine. In fact a product certified under it is required to state that it has not been evaluated for chlorine reduction in the presence of chloramines. The standard itself anticipates exactly this confusion and tries to head it off.

So a shower filter can hold a completely legitimate certification, and that certification says nothing at all about the thing you bought it for. If you want the longer version, we wrote a separate explainer on what these standards actually certify.

Claims worth recognising

We are not going to name brands, because these patterns are everywhere and singling out one company would misrepresent how common they are. Learn the shapes instead:

• Chlorine results presented as chloramine results. The two words look similar and the products perform very differently. Check which one is being claimed.
• “Removes 99%” with no contact time, no flow rate, no incoming concentration and no capacity. A reduction figure without test conditions is not a measurement.
• A certification claim with no standard number. Certification is granted against a specific standard for a specific contaminant list, and a claim that names neither is close to contentless.
• “Tested to” or “meets” or “designed to meet” standing in for “certified to”. These are different things, and the wording is chosen deliberately.
• A real certification cited next to an uncertified claim, so the credibility of one appears to cover the other.
• Media percentage as a proxy for performance. How much KDF a cartridge contains tells you nothing if the water is only in contact with it for two seconds.

What we would actually do

1. Find out what your utility uses. Free, and it determines everything else.
2. If it is free chlorine, an inline shower filter is a reasonable, cheap intervention and the contact time problem largely does not apply to you.
3. If it is chloramine, do not buy a shower filter expecting it to address that. It may still do something useful about other things; it is not the tool for this one.
4. If chloramine specifically is what you want to address, the realistic route is a tank-based catalytic carbon system sized for contact time. That is a sizing statement rather than a product recommendation, and we have not reviewed any such system.

Why there is nothing to buy on this page

You will notice this page has no product recommendation and no affiliate link. That is deliberate.

The honest conclusion is that the product category most people arrive here considering does not solve the problem they arrived with. Attaching a purchase button to that conclusion would contradict the page. We would rather earn nothing here and have you believe the next page.

If you want the neighbouring decision — what a shower filter is actually for, and how it compares to treating your drinking water — that is the comparison next door, and it does carry links we earn from. It also has a section on when neither purchase is warranted.

Written and reviewed by CJ. Last verified 2026-09-03. Next review due 2027-03-03.