Disinfection Byproducts

A chemical molecule with both green and red disinfection byproducts.


Chlorine was discovered in 1774 by the chemist Karl Scheele. One of the first known uses of chlorine for disinfection was not until 1850, when Snow used it to attempt to disinfect London’s water supply during that now-famous cholera epidemic. It was not until the early 1900’s, however, that chlorine was widely used as a disinfectant. Chlorine revolutionized water purification, reduced the incidence of waterborne diseases across the western world, and “chlorination and/or filtration of drinking water has been hailed as the major public health achievement of the 20th century”. Chlorine remains the most widely used chemical for water disinfection in the United States. However, close to 1 billion people in the world still lack access to safe drinking water, and new questions about health effects from chlorine by-products formed during disinfection have led to questions about the advisability of using chlorine to provide safe water for this population. This page summarizes information about the production, and health effects, of disinfection by-products (DBPs).

Chlorine itself can form harmful compounds called Trihalomethanes (THMs) when the chlorine chemically combines with the natural organic substances found in water. These compounds are believed to cause cancer.


1. White, G. The Handbook of Chlorination, 2nd Edition. Van Nostrand Reinhold Company, New York. 1986.
2. Gordon G, Cooper WJ, Rice RG, Pacey GE. Disinfectant residual measurement methods. AWWA Research Foundation, American Water Works Association. 1987.
3. Calderon RL. The epidemiology of chemical contaminants of drinking water. Food Chemical Toxicology. 2000;38:S13-S20.