Health Indicator Report of Drinking Water: Disinfection Byproducts (DBPs)

People drink and use water every day. The majority of Americans are provided with high quality drinking water. About 90% of people in the U.S. (262 million in 2006) get their water from a community water system (CWS) versus a smaller water supply such as a household well. The U.S. Environmental Protection Agency (EPA) sets regulations for treating and monitoring drinking water delivered by CWS. Currently, there are water quality standards and monitoring requirements for over 90 contaminants. Drinking water protection programs play a critical role in ensuring high quality drinking water and protecting the public's health.

Because people drink and use water every day, contaminants in drinking water have the potential to affect many people. The number of people served by a CWS varies from at least 25 people to hundreds of thousands. CWS in the U.S. provide among the highest quality drinking water in the world. However, some contaminants are present at low levels, and it is still possible that drinking water can become contaminated at higher levels. If a person is exposed to a high enough level of a contaminant, they may become ill. Effects can be seen by the duration (time) of the exposure. Short-term or long-term effects depend on the specific contaminant, the level of contaminant in the water, and the person's individual susceptibility. As additional information is obtained about how specific contaminants affect public health, standards may change in order to better protect public health.

In order to ensure the public's safety with regards to drinking water, community water suppliers treat their water with several products including: chlorine, ozone, chlorine dioxide, ultraviolet light, etc. These products that are used to kill pathogens, however, sometimes react with naturally-occurring organic matter, and create disinfection byproducts (DBPs). DBPs for which the EPA has created standards include: total trihalomethanes (TTHM), haloacetic acids (HAA5), bromate, and chlorite. Although the risk of illness from drinking water that has not been disinfected is much higher than illness from DBPs, some increased health risks do occur from consumption of DBPs. Consumption (through inhalation, ingestion, and absorption through the skin) at high levels over a long period of time has been shown to increase the risk of developing bladder cancer. Rectal and colon cancer along with problems involving the liver, kidney, and nervous system have also been shown to have a correlation with those who have been exposed to DBPs over a long period of time.

DBPs are formed when disinfectants are used to inactivate microbial contaminants in water and react with materials, primarily organic matter, in the water. Several hundred DBPs in over a dozen chemical classes have been identified. (Modified from the National Environmental Public Health Tracking Network (NEPHTN) Nationally Consistent Data and Measures (NCDM) DBP indicator document, version 4).

DPB levels tend to be highest in water derived from surface sources because ground water generally has little organic matter. Ground water can, however, produce relatively high levels of the more brominated DBPs when the water, due to either geological circumstances or salt water intrusion in coastal areas, has elevated levels of bromide. (Modified from the NEPHTN NCDM DBP indicator document, version 4).