What Are Trihalomethanes in My Water Report?

The short answer

Trihalomethanes (TTHM) and haloacetic acids (HAA5) are by-products that form when the chlorine or chloramine that disinfects your water reacts with natural organic material. Your utility must keep them under federal limits and lists its results in the annual report. If you’d rather have as little as possible in the water you drink, carbon where water enters the house plus reverse osmosis at the kitchen tap is the combination to look at.

Why they form

Utilities disinfect water to kill bacteria, viruses and parasites, and that protection matters. The trade-off is that disinfectants react with leaves, soil and other natural material in the source water. The longer water travels and the warmer it gets, the more by-products can form.

TTHM and HAA5 explained

TTHM

The total of four compounds: chloroform, bromodichloromethane, dibromochloromethane and bromoform. Limit: 80 parts per billion.

HAA5

The total of five haloacetic acids. Limit: 60 parts per billion.

EPA’s disinfection by-product rules set these limits, and utilities check compliance with running annual averages at specific sampling sites. Disinfection by-products are also one of the four groups on EPA’s 2026 draft watch list.

Reading your utility’s results

Look at the range and the average, the sampling year and whether a violation is listed. One high sample isn’t the same as a violation, because compliance uses averages. If the table is confusing, our report guide walks through it, or ask your utility.

Why a chlorine test can’t answer this

A chlorine strip measures disinfectant. It can’t measure TTHM or HAA5, and neither can smell. For a result from your own faucet, you need a qualified lab.

What reduces them at home

Carbon reduces many disinfection by-products when it has enough capacity and contact time, which is why a full-size carbon tank at the point of entry does more than a small cartridge. Reverse osmosis systems add carbon stages and a membrane for the water you drink. Match any specific claim to the system’s performance data.

How Sunstorm treats the whole home

We use the highest-performing multi-stage media we can buy, size it to your water and household, and add reverse osmosis where you drink.

Every tap

HydroOne or HydroDuo

Catalytic carbon, KDF and 10% cross-linked softening resin treat the water where it enters your home, so every shower, sink and appliance gets filtered, soft water.

See HydroOne →

Kitchen tap

HydroSip RO

Four-stage reverse osmosis under the sink with its own faucet, for drinking water, coffee, cooking and ice.

See HydroSip →

Want RO at every tap? We install Hydro360 whole-home reverse osmosis too. For most homes, filtration and softening plus kitchen RO is the better value: the same drinking water at the sink, without paying to purify the water you shower, flush and wash with. See Hydro360

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Questions homeowners ask

Are trihalomethanes the same as chlorine?

No. Chlorine is the disinfectant. Trihalomethanes are by-products that form when it reacts with natural material.

Does boiling remove trihalomethanes?

Boiling isn’t a practical daily treatment. Carbon filtration is the usual approach.

Does every carbon filter reduce by-products?

No. Media type, size and contact time all matter. Check what the filter was tested to reduce.

Why do results change during the year?

Temperature, organic material in the source, disinfectant dose and how long water sits in the pipes all affect them.