Community water may contain viruses and bacteria that can cause illness, such as gastrointestinal disorders or diarrhea. Community water suppliers disinfect their water to kill these viruses and bacteria. Chlorine is the most commonly used disinfectant, sometimes used in combination with other disinfectants, such as ozone, chloramine, chlorine dioxide, and ultraviolet light.

Disinfection by-products (DBPs) are a family of chemicals formed when these disinfectants react with naturally occurring organic matter and other substances in the source water. The levels of disinfection by-products depend upon the nature of the source water, the type of treatment to remove particles and organic matter, and type and concentration of disinfection. The US Environmental Protection Agency requires that water systems use treatment methods to reduce the formation of disinfection by-products and to protect people from waterborne disease and the potential harmful effects of DBPs.

Disinfection By-Products and Your Health
When people consume disinfection by-products (DBPs) at high levels over many years, they increase their risk of developing bladder cancer. However, the risk of illness from disinfection by-products is much lower than the risk of illness from drinking most surface water and some groundwater sources that have not been disinfected. Other health effects that may be associated with exposure to DBPs include rectal and colon cancer. Adverse developmental and reproductive effects associated with exposure to disinfection by-products during pregnancy are a concern. They have been studied with mixed results; however, the weight of evidence of the health effects data suggests a potential association.

Exposure and Risk
Surface water sources such as reservoirs and streams are more likely to have higher disinfection by-product levels than disinfected groundwater sources. However, in some states (for example, Florida and Texas) where drinking water comes from groundwater with high levels of natural organic material, groundwater is also associated with high levels of DBPs. If you get your drinking water from a private drinking water well, disinfection by-products are unlikely to be present in the water.

There are several ways that disinfection DBPs can get into your body: 

• Ingestion (through your mouth): Drinking water with DPBs
• Inhalation (through your nose): Some DBPs can be released into the air in your home when you use your tap water. This can happen when you are taking a shower or washing dishes. And the hotter the water is, the more likely it is that DBPs will be released into the air. DBPs can also get into the air when you boil your tap water, such as when you make tea or soup.
• Dermal (through your skin): You can be exposed to DBPs when your skin comes into direct contact with water, such as when you are bathing or showering. But for most people, only very small amounts of DBPs get into the body through the skin. However, these amounts can increase to much higher levels as your contact time with water increases, for example, if you typically take long baths or swim frequently in public pools.

If your public water system has notified you of a disinfection by-product (DBP) violation, it does not mean that the people who consume the system's water will become sick. Also, because of the tighter regulations on DBPs that are beginning to go into effect, it does not necessarily mean that your exposure to DBPs has increased.

Tracking Disinfection By-Products
NH EPHT is tracking disinfection by-products in public drinking water. Data about disinfection by-products in public drinking water are currently available on the Environmental Health Data Integration Network (EHDIN).

For more information about DBPs and current regulations:

• NH DES
• EPA

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