Two houses, two towns, the "same" city-water complaint: taste and smell. A dealer installs the same carbon system in both. One customer is thrilled. The other calls back in months, unhappy. Same equipment, same install quality — different disinfectant. The first utility uses free chlorine; the second uses chloramine, and chloramine does not care that a filter handled chlorine well.
If you sell on municipal water, this distinction decides your carbon selection, your sizing, and your callbacks.
Why utilities use each — and why chloramine is spreading
Chlorine is the classic disinfectant: fast-acting and effective, but it dissipates relatively quickly in the distribution system and reacts with natural organic matter to form regulated disinfection byproducts. Chloramine — chlorine bonded with ammonia — is the answer many utilities adopted: it's more stable, persists further into the distribution system, and produces lower levels of those regulated byproducts. That stability is exactly what makes it a harder job at the point of entry: the same persistence that helps the utility resists your filter.
The treatment difference, in practical terms
| Free chlorine | Chloramine | |
|---|---|---|
| Chemistry | Hypochlorous acid/hypochlorite | Chlorine + ammonia (mono/di/tri-chloramine) |
| Stability in pipes | Dissipates faster | Persistent by design |
| Standard activated carbon | Reduces effectively | Slow, partial — undersized beds fall short |
| Best media practice | Standard activated carbon | Catalytic activated carbon |
| Contact time needed | Baseline | Meaningfully more — size bigger, run slower |
| Off-gasses if water sits out? | Somewhat | Barely — persistence again |
Two working rules follow. Rule one: chloramine wants catalytic carbon. Catalytic activated carbon is surface-modified to accelerate the breakdown of the chloramine molecule; standard carbon relies on slower adsorption chemistry and gives up capacity quickly on chloraminated water. Rule two: chloramine wants more contact time. Even with catalytic media, design for a slower service-flow-to-media ratio — a bed that was adequate for chlorine can be undersized for chloramine at the same flow. (The math for both cases is in our carbon sizing guide.)
How to find out which one your customer has
Never guess. Three checks, in order of authority: the utility's Consumer Confidence Report usually states the disinfectant — look for "chloramine" or "chloramination" in the treatment description (how to read a CCR); a phone call to the utility settles it in two minutes; and your own field test kit can distinguish free vs. total chlorine at the tap — a low free-chlorine reading with meaningful total chlorine points to chloramine. Worth knowing: some utilities switch seasonally between chlorine and chloramine. If yours does, design for chloramine — the harder case — year-round.
Why RO makes this a two-stage story
Both chlorine and chloramine attack the thin-film composite membranes used in most residential reverse-osmosis systems — membrane damage from disinfectant is a classic premature-failure mode. Every properly designed RO installation on municipal water puts carbon ahead of the membrane, and on chloraminated water that pre-treatment deserves the same catalytic-carbon-and-contact-time thinking as the whole-home stage. Where the whole house gets a correctly sized carbon system upstream, the RO membrane downstream lives an easier, longer life — one more reason the municipal treatment sequence is ordered the way it is.
Key takeaways
- Chlorine and chloramine are different treatment problems: chloramine is deliberately persistent and resists standard carbon.
- Chloraminated water calls for catalytic activated carbon and more contact time — size bigger, flow slower.
- Identify the disinfectant before quoting: CCR first, utility call second, free-vs-total chlorine field test third; design for chloramine if the utility switches seasonally.
- Both disinfectants damage RO membranes — carbon pre-treatment ahead of any membrane, always.
- Misdiagnosing chloramine as chlorine is a callback machine; getting it right is a differentiator.
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