Disinfection byproducts · in your tap water

Chloroform

The most common trihalomethane

Reviewed by Tyler Griffin — Founder, SwiftPro Heating, Cooling & Plumbing

FamilyDisinfection byproducts

Where it comes fromDisinfection byproduct of chlorine + organic matter

Best fixActivated carbon (whole-home or under-sink)

What it is

Chloroform is the largest single component of TTHMs in most chlorinated water supplies. EPA classifies it as a likely human carcinogen.

If your shower steam smells chlorinated, that's the chloroform aerosolizing. Skin absorption + breathing add to drinking exposure.

What you might notice & the health concern

No taste at typical drinking-water levels
Inhalation exposure during hot showers can be measurable — sensitive people sometimes report headaches after long hot showers
Long-term: liver, kidney, and central nervous system effects in animal studies; human cancer evidence is via the broader TTHM exposure

What actually removes it

Activated carbon (whole-home or under-sink)
Reverse osmosis
Showerhead carbon filters reduce inhalation exposure

Not sure which system you need? Our reverse-osmosis and whole-home pages compare the options, or book a free Home Water Checkup and we'll test your actual tap.

The research

Every source below was checked to make sure the link works and backs the claim it's next to. These are the primary regulators and peer-reviewed studies — not our opinion.

Chloroform ↗ EWG Tap Water Database

EWG health guideline of 0.4 ppb (California OEHHA basis); cancer + fetal harm.

Chloroform — IARC Summary & Evaluation, Vol. 73 ↗ IARC / IPCS INCHEM

IARC classifies chloroform as Group 2B, 'possibly carcinogenic to humans.'

IRIS Chemical Summary — Chloroform (CASRN 67-66-3) ↗ U.S. EPA IRIS

EPA judges chloroform 'likely to be carcinogenic to humans' under high-exposure conditions.

Toxicological Profile for Chloroform ↗ ATSDR / CDC

Liver and kidney are the target organs; documents the animal carcinogenicity data.

Want to know if it's in YOUR water?

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This page is general water-quality education, not medical advice. Health classifications and limits are attributed to the EPA, EWG, IARC, ATSDR/CDC, WHO and the cited studies. Contaminant levels vary by water system and home — the only way to know what's in your water is to test it. Prepared by SwiftPro Heating, Cooling & Plumbing.