Chlorinated Shower Water

Hot showers in chlorinated municipal water.

72Low burden · out of 100

Cleaner swapShorter showers

How this score is built

100Start
90.8Chemical hazard 2 × 4.6−9.2
77.2Everyday exposure 4 × 3.4−13.6
72Persistence 2 × 2.6−5.2
LowThe band72 sits in 60–79.

What each input rests on

The three ratings behind the score, and the studies each rests on
Input	Rating	Evidence
Chemical hazard	2/10	In a New England case-control study, the highest showering/bathing category for brominated trihalomethanes gave a bladder-cancer odds ratio of 1.43 (95% CI 0.80–2.42); the authors concluded a modest association for ingestion. Bladder Cancer and Water Disinfection By-product Exposures through Multiple Routes: A Population-Based Case-Control Study (New England, USA) · Environ Health Perspect 2017 DOI 10.1289/EHP89 · PMID 28636529 · Abstract, Results; Conclusions · read 2026-10-02
Everyday exposure	4/10	In 100 volunteers taking controlled 10-minute showers, geometric mean total trihalomethanes in air rose from 5.8 to 351 μg/m3, and in blood from 16.5 to 299 ng/L. The influence of physicochemical properties on the internal dose of trihalomethanes in humans following a controlled showering exposure · J Expo Sci Environ Epidemiol 2013 DOI 10.1038/jes.2012.80 · PMID 22829048 · Abstract · read 2026-10-02 In a controlled study of six people, 56% of chloroform was released from shower water to air, and inhalation during a typical 10–15 minute shower contributed significantly to total chloroform dose. Human respiratory uptake of chloroform and haloketones during showering · J Expo Anal Environ Epidemiol 2005 DOI 10.1038/sj.jea.7500374 · PMID 15138448 · Abstract · read 2026-10-02
Persistence	2/10	After a 1-hour forearm soak in water containing bromodichloromethane, blood levels fell to near or below detection by 24 hours; after drinking, levels returned near or below detection within 4 hours. Disposition of bromodichloromethane in humans following oral and dermal exposure · Toxicol Sci 2007 DOI 10.1093/toxsci/kfm190 · PMID 17656487 · Abstract · read 2026-10-02

Ratings are editorial. A study listed here supports the rating; it did not compute it. How the index is built

What this means for you

Hot showers release chloroform and other disinfection by-products into the air you breathe, and some are absorbed through the skin. In a volunteer study, one of them, bromodichloromethane, fell to near undetectable blood levels within a day of skin exposure.

Evidence strength: moderate

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