An Integrated Evaluation of Drinking Water Quality and Environmental Planning Implications Using WQI and Exceedance Analysis: Al-Doura Water Treatment Plant, Baghdad

The quality of drinking water is of critical importance to the health of people, especially in river-based supply systems facing the growing environmental uncertainty. Nevertheless, most of the tests are based on coarse indices like the Water Quality Index (WQI) that might fail to capture short-term surpluses and incidental degradation. This paper will provide a combined assessment of drinking water quality in the Al-Doura Water Treatment Plant, Baghdad, Iraq, which receives a direct supply of raw water from the Tigris River. WQI was used to test monthly monitoring parameters of physicochemical key parameters in raw and treated water under mean- and maximum-based exceedance analysis in relation to the World Health Organization standards from January to December 2024. The WQI of treated water (mean = 61.31) is moderate. Mean-based exceedance analysis proves that in the case of average operating conditions, all analyzed parameters are generally compliant with the guideline values. However, extreme turbidity changes in raw water have been described as one of the consistent operational stressors. The maximum-based exceedance analysis further revealed that calcium levels in treated water exceeded the WHO permissible limit by up to 28%, highlighting short-term risks and treatment constraints that remain hidden within aggregated indices, a phenomenon known as the eclipsing effect. By exposing these masked exceedances, the maximum-based approach offers a more reliable early-warning tool than WQI alone for safeguarding public health in river-dependent supply systems.