To provide safe drinking water to urban populations, raw water must be treated in drinking water treatment plants, which are energy-intensive facilities. Previous studies have assessed energy intensity (EI: unit of energy required per unit of treated water) of conventional drinking water treatment plants, but they ignored variations related to water treatment trains. By modeling 179 facilities of four water treatment trains, we explored factors potentially affecting energy intensity, such as removal efficiencies of pollutants and treatment capacities of drinking water treatment plants. We also investigated the economies of scale in energy intensity of drinking water treatment plants. Our results illustrated that the energy intensity of water facilities using pressure filter systems is affected by several pollutant removal efficiencies, but not by plant capacity. In contrast, the volume of water treated is the main factor responsible for the energy intensity in plants using rapid gravity filter systems and, therefore, their energy intensities are significantly affected by economies of scale. The results of this study should be useful to policy makers planning new facilities and developing policies to reduce the carbon footprints of urban water treatment plants. (C) 2017 Elsevier Ltd. All rights reserved.