Enhancing residual chlorine stability in water distribution systems: Challenges, modeling approaches, and advanced optimization strategies

The persistence of residual chlorine in drinking water distribution systems (DWDS) is vital for ensuring microbiological safety and regulatory compliance. However, accurately predicting and controlling chlorine decay remains a major challenge due to the complex interplay of physical, chemical, hydraulic, and infrastructure-related factors. This review provides a structured and critical evaluation of chlorine decay mechanisms—bulk and wall decay—across varying supply regimes, particularly in the context of intermittent water supply (IWS) systems common in developing regions. The core objective of this work is to assess the factors influencing chlorine stability and to evaluate the performance of traditional kinetic and emerging artificial intelligence (AI)-based models in diverse operational conditions. A systematic literature review methodology was employed, retrieving 312 studies and analyzing 97 peer-reviewed sources from global databases. The reviewed literature was thematically classified to explore decay parameter estimation, software tools, pipe material impacts, and the role of AI-enhanced predictive modeling. The novelty of this study lies in its integrated comparison of conventional and AI-driven decay models, the quantitative synthesis of decay coefficients under varying climatic and operational conditions, and a contextual analysis of IWS vs. continuous supply systems, which are often underrepresented in the literature. Additionally, the review identifies critical modeling gaps such as poor field validation, lack of climate sensitivity, and limitations in existing software platforms, and proposes future directions for hybrid model development and smart utility integration. By synthesizing diverse modeling approaches and real-world case studies, this review provides a scalable and adaptable framework to enhance chlorine retention strategies, inform infrastructure planning, and support the transition toward resilient, data-informed water quality management systems globally. • Comprehensive Analysis of Chlorine Decay Mechanisms. • Evaluation of Chlorine Decay Models. • Impact of Intermittent vs. Continuous Water Supply on Chlorine Stability. • Technological Advancements in Chlorine Optimization. • Future-Oriented Strategies for Sustainable Water Management.