There's Something in the Water! A Look at Disinfection By-products in Drinking Water

Author:  Vora Sadhna
Institution:  Chemistry
Date:  September 2005

I took a long gulp of fresh, cold water when I staggered into my apartment. It was one of those suffocating summer days in Washington D.C, when the heat blankets your body and only an ice-cold cup of water promises escape. I splashed some on my face, collapsed on the couch, and began thumbing through a pile of journal articles on disinfection of drinking water - homework for my job as an environmental health intern at Physicians for Social Responsibility.

Water disinfection, which reduces microbial contamination, is among the greatest triumphs of public health in the twentieth century. Illnesses such as typhoid fever and cholera can now be prevented by modern sanitation processes. However, our current methods of disinfection trade one set of drinking water contaminants for another. The rest of my glass of water stood untouched as I read the research articles on disinfection by-products (DBPs), toxic substances such as trihalomethanes, haloacetic acids, bromate and chlorite that form when disinfectants react with organic material naturally found in water (EPA Office of Water 2001).


The Effects of Drinking Water DBPs on Public Health

Chlorination, which produces a number of harmful DBPs, is the most common method of disinfecting water (Farland et al. 1993). Some DBPs cause developmental and reproductive defects, while others damage the heart, brain, kidneys and liver (Tibbets 1995). Residual chlorine and chlorination by-products are also human carcinogens. According to the U.S. Council of Environmental Quality, the cancer risk to people who drink chlorinated water is 93% higher than among those whose water does not contain chlorine (Environmental Systems Distributing 2000). Cancers of the colon, rectum and bladder have been linked to chlorinated drinking water (Hildesheim 1998). One study estimated that chlorination by-products result in 10,700 bladder and rectal cancers a year (Tibbets 1995); another suggested a possible correlation between certain DBPs in drinking water and breast cancer (Melnick 1994).

DBPs pose a particularly grave risk for young children. The reason for this heightened risk is two-fold. First, children consume much more water per unit of body weight than adults, and are therefore exposed to higher levels of DBPs. Second, children's bodies are more susceptible to injury from toxins. A study by Kanitz et al. (1996) shows that a given quantity of a DBP more strongly affects a child's body than an adult's. The chlorates and chlorites that form during disinfection are especially toxic to children. Infants' and young children's blood cells are relatively easily damaged by these substances, resulting in a reduced ability to transport oxygen throughout the body.

Kanitz's group also provided evidence that DBPs have strong effects on fetuses. They found that jaundice was nearly twice as likely to occur in newborns whose mothers drank water disinfected with chlorine dioxide during pregnancy. The newborns were also more likely to have a smaller body length and head size if their mothers had consumed chlorinated water during pregnancy.

Trihalomethanes are another class of DBPs that result when chlorine is used as a disinfectant. Studies have linked these DBPs with an increased frequency of stillbirths (King 2000). Trihalomethanes have also been implicated in birth defects of the brain and spinal cord (Klotz 2000). Babies with these defects may die soon after birth or may demonstrate learning disorders or mental retardation.

While chlorination is a common means of disinfection, there are other methods also currently in use. Ozonation, a process that uses the tri-atomic form of oxygen as a disinfectant, is the most common alternative to chlorination. Although ozonation does not give rise to the creation of trihalomethanes and other chlorinated by-products, it creates other DBPs under certain conditions. The most prevalent ozonation DBP is bromate, a toxic product of chemical reactions initiated by ozone in bromide-containing waters. Bromate ingestion can cause abdominal pains, kidney failure, hearing impairment and an increased risk of cancer (SFPUC 2000).


How are Drinking Water DBPs Regulated?

In order to limit the effects of DBPs, the Environmental Protection Agency (EPA) has implemented standards that regulate the concentrations of both DBPs and organic materials (such as bromide) that react with disinfectants to produce DBPs (EPA 2001). In 1996, the Safe Water Drinking Act mandated that the EPA set enforceable standards to protect drinking water quality (Federal Advisory Committee, EPA 2000). This law sought to regulate not only DBPs, but also a host of other drinking water contaminants. The first step was to assess the status of drinking water in the United States. Massive data collection on drinking water systems led to the Stage 1 Disinfectants and Disinfection By-Products Rule, limiting maximum acceptable levels of DBPs such as bromate and total trihalomethanes. Large systems must comply with this rule by 2002 and smaller ones by 2004. Meeting these standards is expected to cost $700 million and provide 140 million people with increased protection from DBPs (EPA 2001). The EPA is considering even more stringent measures for the future. Clearly, the government views DBPs as a noteworthy risk to public health in the U.S.


What Can You Do to Protect Yourself?

An important step towards protection is becoming informed. Read your water provider's consumer confidence report, and familiarize yourself with the health effects of known or likely contaminants in your area. Contact your water company to find out if they have done a source water assessment, a sanitation survey, or any other review of DBPs. If not, urge your water utility to complete these studies. Inquire about the water treatment processes used in your communities, and ask how chlorination is used in the sanitation process, if it is.

All individuals who consume drinking water contaminated with DBPs risk long-term health effects, but children, the elderly, pregnant women, and people with suppressed immune systems face especially high risks. The hazards posed by disinfectant by-products can be reduced by consuming bottled water or better yet, by using a personal water filter.

My internship at PSR made me aware of important environmental health risks such as DBPs. Although the likelihood of DBP poisoning is relatively small in comparison with the public health hazards of microbial contamination, it nonetheless deserves consideration since more than 200 million people in the United States consume disinfected drinking water. The issue calls for greater attention by the scientific and health care communities to processes of drinking water disinfection. Scientific research may one day lead to new technology and techniques that will render drinking water safer from both microbial and chemical risks. But until that day comes, I suggest investing in a water filter!

Suggested Reading

Environmental Systems Distributing. "Things you should know about your drinking water and municipal tap water". Fact sheet. 2000. Available online at:

EPA Office of Water Website.

EPA Office of Water. "Drinking Water Priority Rulemaking: Microbial and Disinfection Byproduct Rules". Fact sheet. 2001. Available online at:

Farland, WH, Gibb, HJ. EPA. "U.S. Perspective on Balancing Chemical and Microbial Risks of Disinfection". Safety of Water Disinfection: Balancing Chemical & Microbial Risks edited by Craun, GF. ILSI Press. Washington, DC. 1993. pp. 3-16.

Federal Advisory Committee, EPA. "Stage 2 Microbial/Disinfection Byproducts". 2000. Available online at:

Hildesheim, ME, et al. "Drinking Water Source and Chlorination By-products I. Risk of Bladder Cancer". Epidemiology. 1998. 9(1): 21-28.

Hildesheim, ME, et al. "Drinking Water Source and Chlorination By-products II. Risk of Colon and Rectal Cancer". Epidemiology 1998. 9(1): 29-35.

Kanitz, S, et al. "Association between Drinking Water Disinfection and Somatic Parameters at Birth". Environmental Health Perspectives 1996. 104(5).

King, WD, et al. "Relation between Stillbirths and Specific Chlorination By-Products in Public Water Supplies". Environmental Health Perspectives 2000. 108(9).

Klotz, JB, Pyrch LA. "Neural Tube Defects and Drinking Water Disinfection By-Products." Epidemiology 1999. 10(4): 383-390.

Marcus, PM. "Female breast cancer and trihalomethane levels in drinking water in North Carolina". Epidemiology 1998. 9(2): 156-60.

Melnick, RL. "Trihalomethanes and Other Environmental Factors that Contribute to Colorectal Cancer". Environmental Health Perspectives 102(6-7) 1994. Available online at:

San Francisco Public Utilities Commission (SFPUC). "Water Quality Fact sheet: Chemical Risk Topics, Bromate". Fact Sheet. 1999, 2000. Available at:

Tibbets, John. "What's in the Water: The Disinfectant Dilemma." Environmental Health Perspectives 1995. 103(1) Available at:

Sources of Additional Information and Guidance

* Physicians for Social Responsibility: (202) 667-4260 or

* Campaign for Safe and Affordable Drinking Water

* U.S. EPA Office of Ground Water and Drinking Water: (202) 260-5543 or

* National Drinking Water Advisory Council

* National Academy of Sciences

* National Resources Defense Council

* Environmental Working Group

* U.S. Public Interest Research Group (U.S. PIRG)