The incidence of waterborne diseases has been greatly reduced since the widespread implementation of drinking water disinfection and enactment of the Safe Drinking Water Act (SDWA) in 1974.  Unfortunately, however, disinfectants like chlorine, ozone, bromine and chlorine dioxide can also pose health risks. 

The disinfectants themselves can react with organic materials in the water to form byproducts. Other factors in the formation of DBPs include the type of disinfectant, application point in the treatment process, type and concentration of organic matter in the water, pH, temperature and contact time with the disinfectant. An important question facing water supply professionals is how to minimize the risk from both microbial pathogens and disinfection byproducts simultaneously.  

Water customers can monitor and track the amount of DBPs in their drinking water through the water system’s Consumer Confidence Report. Customers should contact the water system for a copy of the report.     

Trihalomethanes  

What are Trihalomethanes?  

Trihalomethanes (THMs) are small organic compounds similar in structure to methane, but also containing chlorine and/or bromine. The compounds are the major byproducts of chlorine disinfection of water supplies. They are formed when naturally occurring organic substances react with chlorine used to disinfect drinking water. The trihalomethanes of significance in disinfected water are chloroform, dichlorobromomethane, chlorodibromomethane and bromoform.  

What are the Health Effects of THMs?  

The health effects of THMs are unclear. Studies of human populations have indicated a slightly higher incidence of bladder and colon cancer in areas where the drinking water has been chlorinated. Other studies, however, have not shown an increased risk of cancer. While animal studies have shown mutagenic and carcinogenic potential of THMs, it has been suggested that these results are unreliable since the animals are exposed to THM levels 10,000 times greater to which humans are exposed. Some epidemiological studies have found associations between adverse reproductive outcomes and consumption of drinking water high in THMs, and some have not detected the associations. Studies continue to be conducted to better define whether there is a link between consumption of drinking water high in THMs and the risk of low birth weight or other adverse effects on pregnancy.  

How may I be Exposed to THMs?  

THMs are found in disinfected drinking water supplies. The levels of THMs are dependent on the amount of naturally occurring organic material found in the source water and the amount of chlorine used in disinfection.  

Are the Levels of Trihalomethanes in Drinking Water Dangerous to my Health?   

Several epidemiology studies have suggested a weak association between exposure to chlorinated surface water and certain cancers, reproductive and developmental effects. Because of the large population exposed to chlorinated drinking water, the health risks associated with THMs, even if small, need to be taken seriously.  For this reason, the limit for THMs was reduced from 100 µg/L to 80 µg/L under the Stage 1 Disinfectant and Disinfection Byproducts Rule.

Haloacetic Acids     

What are Haloacetic Acids?  

Haloacetic acids (HAAs) are organic compounds containing chlorine and/or bromine. The compounds are formed from naturally occurring organic substances during chlorination. The HAAs of significance in disinfected water are chloroacetic acid, dichloroacetic acid and trichloroacetic acid, as well as some brominated forms.  

What are the Health Effects of Haloacetic Acids?  

Animal studies have demonstrated that dichloroacetic acid causes adverse effects on the brain, testes and eyes. Less is known about trichloroacetic acid and the brominated acids.  

How may I be Exposed to Haloacetic Acids?  

Low levels of haloacetic acids are present in chlorinated drinking water supplies due to the presence of naturally occurring organic matter, particularly amino acids, in source water, which reacts with chlorine.  

Are the Levels of Haloacetic Acids in Drinking Water Dangerous to my Health?  

The results of toxicity tests suggest that safe levels of HAAs in water for adults consuming two liters of water a day are 420 µg/L for dichloroacetic acid and 175 µg/L for trichloroacetic acid. The Environmental Protection Agency (EPA) regulations limit the total level of HAAs (5 types) to 60 µg/L.  Remember, the concern is over long-term exposure. 

For further information, call the EPA Safe Drinking Water Hotline at 800-426-4791.  You may also find answers to questions on their frequent questions page.

On the Internet, refer to these Web sites:

Click on Disinfection Byproducts: http://www.epa.gov/safewater/hfacts.html

List of contaminants and maximum contaminant levels (MCLs): http://www.epa.gov/safewater/mcl.html  (Scroll down to Disinfection Byproducts.)

Requirements of the public notification (PN) rule: http://www.epa.gov/safewater/publicnotification/compliancehelp.html:   This site contains the PN handbook that tells water systems how they are to notify their customers and exactly what language they must use.