What are DBPs?
Before any treatment, public drinking water may contain viruses and bacteria that can cause illness, such as gastrointestinal disorders or diarrhea. Chlorine is often added to kill these pathogens. Sometimes other disinfectants, such as ozone, chloramine, chlorine dioxide, and ultraviolet light, are also used. While effective, chlorine-based disinfectants can react with naturally occurring substances in the water and form byproducts, called disinfection byproducts (DBPs). The levels of DBPs depend on whether the source water is surface water or groundwater, the type of treatment used to remove particles and organic matter, and the specific disinfectant and its concentration.
Haloacetic acids and trihalomethanes are two groups of DBPs. The combined concentration of five regulated haloacetic acids (monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monobromoacetic acid, and dibromoacetic acid) are referred to as HAA5 and that of four trihalomethanes (chloroform, bromoform, bromodichloromethane, and dibromochloromethane) are referred to as total trihalomethanes (TTHM).
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?
While exposure to DBPs can affect health, the risk of harm is much lower than that from waterborne diseases like cholera that can occur in untreated contaminated drinking water. The degree of risk for health effects depends on the levels of DBPs and duration of exposure.
Effects on the liver, kidneys, and reproductive system have been reported in laboratory animals exposed to high levels of HAA5 and TTHM. Developmental effects have also been reported for HAA5 and neurological effects for TTHM.
Both TTHM and HAA5 are possibly carcinogenic to humans based on evidence of carcinogenicity 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 Maximum Contaminant Levels (MCLs) are 0.08 milligrams per liter (um/L) for THM and 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, the number of treatment plants, historical DBP levels, and the size of the population served.
Systems that use surface water sources test more frequently because surface water contains more materials that may react with the disinfectants, possibly leading to 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.