The occurrence of trihalomethanes (THMs) and haloacetonitriles (HANs) in three water distribution networks (Thapra, Kota, and Khon Kaen University (KKU)) in Khon Kaen Municipality, Thailand, from November 2015 to December 2016 was investigated. The highest THMs and HANs were 584 μg/L and 30 μg/L, respectively. Chloroform was the dominant species of the THM pool and trichloroacetonitriles were the dominant species for HANs. Water treatment plants using free chlorine (Thapra and Kota) formed more THMs than the plant using ClO2 (KKU). In the summer season, more brominate THMs were observed. In many locations, total THM concentrations were found to be higher than the drinking water standard of the Provincial Water Authority of Thailand. The concentration of THMs tended to increase with greater distance from the water plants (as water aged), while HAN concentrations decreased with distance, potentially because they were undergoing hydrolysis in the pipeline.

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