Disinfection By-Products

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).

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.

EPA’s Disinfectants and Disinfection Byproducts Rules

The Stage 1 Disinfectants and Disinfection Byproducts Rule (DBPR) reduces drinking water exposure to disinfection byproducts. The Rule applies to community water systems and non-transient non-community systems, including those serving fewer than 10,000 people that add a disinfectant to the drinking water during any part of the treatment process.

The Stage 2 DBPR strengthens public health protection by tightening compliance monitoring requirements for Trihalomethanes (TTHM) and Haloacetic acids (HAA5). The rule targets public water systems (PWSs) with the greatest risk.

Related Information: In-Depth Analysis: Stage 2 DBPR and Consecutive Systems Compliance

Challenge: Taken together, the Stage 1 and Stage 2 Disinfectants and Disinfection Byproducts Rules (DBPRs) improve drinking water quality. The rules do this by providing protection from disinfection byproducts. Byproducts, if consumed in excess of EPA’s standard over many years, may increase health risks.

Drinking water comes from source water locations such as:
Reservoirs, and
Ground water aquifers.

Pathogens, such as Giardia, Cryptosporidium, and viruses, are often found in source water and can cause gastrointestinal illness. Illnesses include diarrhea, vomiting, cramps and other health risks. In many cases, water needs to be disinfected to inactivate (or kill) these microbial pathogens. However, disinfectants can react with naturally-occurring materials in the water to form byproducts including:
Trihalomethanes (THM),
Haloacetic acids (HAA),
Chlorite, and

EPA has developed the DBPRs to limit exposure to these disinfectant byproducts.

Click here for EPA’s Maximum Contaminant Level (MCL) Chart

Click here for Cumming’s Drinking Water Quality Report