What Is It & How Does It Get Into Water?

Trihalomethanes (THMs) are four chemicals — chloroform, bromodichloromethane, dibromochloromethane, and bromoform — that form when chlorine reacts with organic matter. They are classified as probable human carcinogens.

THMs form during treatment when chlorine interacts with organic matter. Levels tend to be higher in warmer months and surface water systems.

Health Effects From Shower Exposure

• Inhalation: THMs are volatile — hot showers release them as gas. Bathroom air levels can exceed outdoor standards during a 10-minute shower
• Skin absorption: THMs readily penetrate skin, with studies showing significant blood-level increases after showering
• Cancer risk: EPA classifies as probable carcinogens. Associated with bladder, colon, and rectal cancer
• Reproductive effects: Linked to increased risk of miscarriage and birth defects

Regulatory Standards & Health Guidelines

Filtration Methods That Remove It

How Afina Shower Filtration Can Help

Afina's multi-stage filtration system uses activated carbon and KDF-55 media to reduce chlorine, heavy metals, and other contaminants — helping protect your skin, hair, and overall health.

Cities Most Affected

While this contaminant can be found in water systems nationwide, these areas tend to have higher levels:

• New York, NY
• Houston, TX
• San Diego, CA
• Tampa, FL
• New Orleans, LA

Check your local water quality at the EWG Tap Water Database by entering your zip code.

Related Reading

• water quality in Houston, Texas
• water quality in Phoenix, Arizona
• water quality in Philadelphia, Pennsylvania