What are DBPs?
Before public drinking water is treated, it may contain viruses and bacteria that can cause illness like gastrointestinal disorders or diarrhea. Chlorine is often added to kill these pathogens. Sometimes other disinfectants are used. Examples include ozone, chloramine, chlorine dioxide, and ultraviolet light.
While effective at killing pathogens, chlorine-based disinfectants can react with naturally occurring substances in the water and form byproducts. These are called disinfection byproducts (DBPs). The levels of DBPs depend on many factors. For example, whether the source water is surface water or groundwater will affect the levels of DBPs. Levels are also affected by the type of treatment used to remove particles and organic matter, and the specific disinfectant and its concentration.
Regulations balance the need for effective disinfection against the risk of harm from DBPs. Haloacetic acids and trihalomethanes are two groups of regulated DBPs.
- HAA5 refers to the combined concentration of five specific haloacetic acids. These are monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid.
- Total trihalomethanes (TTHM) refers to the combined concentration of four trihalomethanes. These are chloroform, bromoform, bromodichloromethane, and dibromochloromethane.
How can I be exposed to DBPs?
People can be exposed to DBPs when drinking or eating food or ice prepared with water that has been treated with a disinfectant. Some DBPs, such as HAA5, can be absorbed through the skin during handwashing, bathing, showering, or swimming. Other DBPs, such as TTHM, can be breathed in from the air, particularly during showering and bathing. After exposure, DBPs remain in the body for a short period of time.
How can DBPs affect my health?
The risk of harm from DBPs is much lower than the risk of consuming waterborne diseases found in untreated drinking water. The degree of risk for health effects depends on the levels of DBPs and duration of exposure.
Exposure of laboratory animals to high levels of HAA5 and TTHM has been shown to affect the liver, kidneys, and reproductive system. Developmental effects were also reported for exposure to high levels of HAA5. Neurological effects were also reported for exposure to high levels of TTHM.
Both TTHM and HAA5 are possibly carcinogenic (cancer-causing) to humans. This is based on evidence in laboratory animals and limited evidence in people. More specifically, animal studies have shown a possible link between long-term exposure to TTHM and liver and kidney cancers.
What is the drinking water standard for DBPs?
The EPA and Massachusetts Department of Environmental Protection (MassDEP) Maximum Contaminant Levels (MCL) is 0.08 milligrams per liter (um/L) for TTHM. The MCL is 0.06 mg/L for HAA5.
What are the testing requirements for DBPs?
All public water systems that use chlorine or ozone to disinfect their water are required to test for DBPs. Testing requirements vary based on:
- Source water type
- Treatment type
- Number of treatment plants
- Historical DBP levels
- Size of the population served
Systems that use surface water sources test more frequently than those that use groundwater sources. This is because surface water contains more materials that may react with the disinfectants and possibly cause higher levels of DBPs.
Systems with surface water sources test between one sample per year per treatment plant to four samples per quarter per treatment plant. Systems with only groundwater sources test either one sample per quarter per treatment plant or one sample per year per treatment plant. The frequency depends on the number of people served by the PWS.
Available data
Use the Explore drinking water data link on this page to access the following measures for DPBs in drinking water:
- Annual maximum concentration by number of Community Water Systems and people served
- Annual average concentration by number of Community Water Systems and people served
- Annual average concentration by Community Water System
- Quarterly average concentration by number of Community Water System and people served
- Drinking water violations by Community Water System
MA EPHT presents data on the following geographies: city/town, county, EP region, or EOHHS region. Data are presented for public water systems only. The most current available data will be shown. Be sure to check the site periodically as new data are added.
Additional resources
Massachusetts
- MassDEP haloacetic acids and total trihalomethane in drinking water information for consumers: Fact sheet on the two groups of DBPs commonly tested in drinking water
- MassDEP home water treatment devices: Information on point of entry (POE) and point of use (POU) drinking water treatment devices
National
- Agency for Toxic Substances and Disease Registry (ATSDR) ToxFAQs on chloroform: Frequently asked health questions about chloroform (one of the four TTHM)
- Agency for Toxic Substances and Disease Registry (ATSDR) ToxFAQs on bromoform and dibromocloromethane: Frequently asked health questions about bromoform and dibromochloromethane (two of the four TTHM)