Evaluation of the Efficiency of Drinking Water Treatment Plants Using the Heavy Metal Pollution Index in Hawija District, Kirkuk, Iraq

Abstract

The aimed study to assess the concentrations of some heavy metals (Pb, Cr, Cd, Ni) in drinking water of three plants in the Hawija Distric, Kirkuk Governorate, Iraq in November 2025, using a atomic absorption spectrometer. Removal efficiency was determined, and water quality was evaluated using a heavy metal pollution index (HPI). The results showed that the lead and cadmium concentrations after treatment remained above the limits permitted by the World Health Organization (WHO) at all stations, while nickel and chromium concentrations remained within the permissible limits. Removal rates ranged between 68.47–73.76% lead, 64.03–69.20% chromium, 54.92–62.20% cadmium, and 60.29–60.86% nickel. The results showed a renewed increased in metals concentrations within the distribution network compared to the treated water, indicating the occurrence of secondary contamination within the network. The pollution index values after treatment between (104.3–116.9), but they remained above the critical threshold (100), then rose to between (142.7–162.5) in the distribution network. The results indicate that the treatment plants were highly effective in reducing the concentrations of the studied metals. however, they were insufficient to achieve safe levels according to the HPI index. Consequently, the study emphasizes the need to upgrade treatment systems for heavy metals removal particularly lead and cadmium and to ensure the periodic maintenance of distribution networks to minimize drinking water contamination.