The occurrence of chlorine dioxide (ClO2) disinfection by-products (DBPs) in drinking water, namely, chlorite, chlorate, and trihalomethanes (THMs), was investigated. Two-hundred-ninety-four drinking water samples were collected from seven desalination plants (DPs), four reservoirs (R), and eight mosques (M) distributed within various locations in southern and northern Qatar. The ClO2 concentration levels ranged from 0.38 to <0.02 mg L−1, with mean values of 0.17, 0.12, and 0.04 mg L−1 for the DPs, Rs, and Ms, respectively. The chlorite levels varied from 13 μg L−1 to 440 μg L−1, with median values varying from 13 to 230 μg L−1, 77–320 μg L−1, and 85–440 μg L−1 for the DPs, Rs, and Ms, respectively. The chlorate levels varied from 11 μg L−1 to 280 μg L−1, with mean values varying from 36 to 280 μg L−1, 11–200 μg L−1, and 11–150 μg L−1 in the DPs, Rs, and Ms, respectively. The average concentration of THMs was 5 μg L−1, and the maximum value reached 77 μg L−1 However, all of the DBP concentrations fell within the range of the regulatory limits set by GSO 149/2009, the World Health Organization (WHO), and Kahramaa (KM). © 2016 Elsevier Ltd
