Abstract-This study aims to investigate the concentration, lifetime cancer risk, and hazard index of trihalomethanes (THMs) through oral ingestion, dermal absorption and inhalation exposure from tap water of 17 community water treatment plants in northeastern Thailand. Chloroform (CHCl 3 ) was found at highest level compared to dichlorobromomethane (CHCl 2 Br), chlorodibromomethane (CHClBr 2 ) and bromoform (CHBr 3 ) species. Results revealed that the Chongsammoe water treatment plant in Chaiyaphum province was found in the highest levels of 48.46 µg/L for total THMs whereas the levels were below the water quality guideline of WHO. Among the three pathways studies, the highest lifetime cancer risk comes from oral ingestion followed by dermal absorption and inhalation exposure route, mainly because of the exposure to CHCl 3 . Overall 6 of 17 plants, the lifetime cancer risk for CHCl 2 Br and CHCl 3 through oral ingestion route were higher than risk level of 10 -6 , the negligible defined by the USEPA. The average hazard index of total THMs in all muti-pathway exposure routes was lower than 1 indicating to acceptable non-carcinogenic risk level.Index Terms-Cancer risk assessment, trihalomethanes, Thailand, water supply. I. INTRODUCTIONWater supply sector is play a major role of economy growth and social well being. The inadequate access to clean water is directly combined with the lack of basic sanitation. The Millennium Development Goal aims at by 2015; the proportion of the world population would sustainable access to safe drinking water. In Thailand, the surface water resource is the core importance of water supply for community that the total volume of water from the rainfall in all river basin of about 800,000 million m 3 . The estimated for the use of improve drinking water sources was 97% of the country which both of 48% on the proved piped water system and other improved water sources [1]. The water treatment systems in Thailand are organized by four organizations: 1) the metropolitan waterworks authority responsible for the Metropolitan Bangkok Region, and the provincial waterworks authority responsible to the major city of the country, the rural water supply is operated by the local authority and the private water treatment plant. The water Manuscript received April 25, 2013; revised June 25, 2013. This work was financial supported by the National Research Council of Thailand.Prapat Pentamwa, Benchamaporn Sukton, and Tanisa Wongklom are with the School of Environmental Health, Institute of Medicine, Suranaree University of Technology, Nakorn Ratchasima, 30000 Thailand (e-mail: prapat@sut.ac.th, ben_sukton@hotmail.com, koryaa_0332@hotmail.com).Sathaporn Pentamwa is with the Health Center 5, Department of Health, Ministry of Health, Nakorn Ratchasima, 30000 Thailand (e-mail: sathapornounchit@hotmail.com).sources of water treatment systems were commonly taken from surface water and underground water. The surface water supply was typically consisted of the coagulation-flocculation, filtration and disinfectio...