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TRIHALOMETHANE (THM) FACT SHEET
(Prepared by the AWWA (American Water Works Association))
What are trihalomethanes (THMs)?
THMs and other disinfection by-products are formed when disinfectants such as chlorine
- used to control disease-causing contaminants in drinking water - react with naturally
occurring organic matter in the source water. The primary trihalomethanes of concern are:
Chloroform Dibromochloromethane
Bromodichloromethane Bromoform
What are THMs in the drinking water?
THMs are result of disinfecting water, which is essential for protecting consumers for
life threatening diseases. The health risks from THMs are extremely small compared to
risks associated with inadequate disinfection. It is important, therefore, that
disinfection not be compromised in an attempt to decrease such by-products.
How do you know if there are THMs in drinking water?
THMs may be present in most drinking waters, including some bottled and home filtered
water. To find out if THMs are in your tap water, call your local water utility. For
bottled water and home filtered water, check on the label or call the manufacturers.
Consumers can also test their own water for THMs by consulting a pre-approved, authorized
laboratory in their state. For a listing of these laboratories, call the Environmental
Protection Agency (EPA) Drinking Water Hotline (1-800-426-4791).
Are THMs monitored or regulated?
Yes. The EPA currently regulates trihalomethanes by imposing a maximum allowable level
in drinking water of 100 parts per billion on the average. To reduce potential exposure,
EPA has proposed to lower that level in the future to an average of 80 parts per billion.
What about pregnant women. Should they be concerned?
Women in the early stages of pregnancy may wish to consult their physicians for advice.
However, health officials who reviewed the THM study agreed that in general they do
NOT advise women in early pregnancy to stop drinking water from public supplies.
How can THM exposure be minimized?
THM levels in tap water can be minimized by boiling it for one full minute and letting
it cool before drinking or by using a home treatment device that is officially certified
by the NSF International as effective to remove THMs.
Where can you get more information?
You can call the Dare County Water Department at (252) 441-7788 to answer any questions
that you may have about disinfection by-products, trihalomethanes and many other drinking
water subjects.
The EPA Drinking Water Hotline (1-800-426-4791) is available to answer questions on
this subject and other water related subjects. This hotline operates from 9:00 am to 5:00
pm EST, Monday-Friday. Brochures and other materials can be requested through the hotline.
Additionally the Office of Ground Water and Drinking Water at EPA maintains a website with
much useful information on drinking water. The address is http://www.epa.gov/OGWDW
Additional information can be obtained by accessing the American Water Works
Association's web site at http://www.awwa.org.
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