The occurrence of trihalomethanes (THMs) in the water supply in the Ankara, Turkey was investigated. Total THMs and total organic carbon measurements were carried seasonally in the samples collected form 22 different districts along with the samples taken from the Ivedik Water Treatment Plant serving 90% of the city. The average summer nonpurgeable organic carbon (NPOC) concentration in the raw water was 4.2 mg/L, and the NPOC removal achieved in the treatment plant was 31%. The concentration of total THMs ranged from 25 to 74 mug/L, from 28 to 73 mug/L, and from 25 to 110 mug/L in winter, spring, and summer, respectively. In all of the samples chloroform existed at the highest concentrations, while bromoform was almost absent. The total THM concentrations were highest in summer for all districts. However, none of the concentrations detected exceeded the USEPA's Stage I limit of 80 mug/L and the EU's limit of 100 mug/L. However, the total THM level in 64% of the districts exceeded the USEPA's Stage II limit of 40 mug/L. The risk estimations carried out indicated that each year 1 of the 5 million Ankara residents could get cancer from the daily intake of water, mainly because of exposure to chloroform through oral ingestion. (C) 2004 Elsevier Inc. All rights reserved.