Evaluation of Residual Chlorine Concentration in the Water Distribution Networks: An Analytical Study

Introduction/Objective Chlorine is considered one of the most important disinfectants due to its widespread availability and moderate cost in most regions of the world. The presence of chlorine in various water supply networks is crucial to ensuring water and sanitation. The aim of this research is to determine the residual chlorine concentration in the water distribution network of the Central Water Project in Baquba and in some of its affiliated areas across Diyala Governorate, Iraq. Five lines are selected within the distribution network, where each line supplies multiple areas, and each line is located in a specific direction within the project's regions. These areas are situated at different distances from the central water project to assess the presence of residual chlorine in drinking water within the permissible limits. The residual chlorine concentration is therefore measured, along with determining the concentrations of relative factors affecting residual chlorine, including the acidity, water temperature, turbidity, and electrical conductivity. Methods To achieve this aim, ninety water samples were collected during the study period from November 2022 to May 2023. Local maps were also created using a Geographical Information System (GIS) to determine the spatial distribution of the stations sampled across the five lines for physical and bacteriological examinations. Results The associated results indicated the existence of efficient chlorine management in some tested periods. However, the ends of the distribution lines introduce a clear challenge of maintaining consistent residual chlorine concentrations. Essential parameters like distance from chlorine sources, temperature, pH, turbidity, and old pipe infrastructure have worsened the reduction of chlorine, emphasizing the need for enhanced water quality management in the distribution network. Discussion The results indicate that while residual chlorine levels can be effectively managed near chlorine sources during certain periods, maintaining stable disinfection actions at the ends of distribution lines remains a persistent challenge. The realised effects of main factors such as temperature, pH, turbidity, distance, and aged pipe infrastructure suggest that chlorine decay is not driven by uniform conditions across the network. This, in turn, underscores the need for more proactive, adaptive water quality management strategies, such as enhanced monitoring, targeted dosing, and infrastructure-focused interventions, to ensure reliable microbial control throughout the distribution system, not only at upstream locations. Conclusion The research indicated that the most polluted areas in Baquba City, Iraq, particularly lines 3, 4, and 5, suffer from bacterial contamination due to zero residual chlorine levels.