Achieving Biological Stability in Drinking Water Supply Systems

Achieving biological stability in drinking water supply systems is crucial for the delivery
of aesthetically pleasing, safe drinking water. Uncontrolled growth of microorganisms can
have aesthetic and health consequences for consumers and generate significant cost for water utilities. This thesis aims to assess biostability from treatment to tap in order to inform key water treatment and distribution practices that will lead to aesthetically pleasing, safe drinking water. By integrating historical data analysis, mathematical modelling, and a robust sampling campaign across five operational DWSS across the UK, this research advances the understanding of microbial dynamics in drinking water. A novel aspect is demonstrating that flow cytometry is an effective and repeatable tool for monitoring biostability at the customer’s tap, capturing changes in cell counts and microbial growth from the point of treatment to the point of consumption. Through analysis of two large historic flow cytometry datasets and an intense sampling campaign, this research reveals the significant impact of distribution systems on biostability, showing that parameters like water age, temperature, disinfection and AOC
concentration exert substantial impact over microbial growth and water quality deterioration from treatment to tap. The study also compares microbial growth patterns in both bench-top experiments and real-world operational conditions, evaluating the feasibility of using mathematical models to predict microbial growth in DWSS. Furthermore, this work provides the first detailed correlation between biostability, customer satisfaction, and compliance with regulated water quality parameters, reinforcing the importance of biostability in ensuring both safe and aesthetic pleasing drinking water. The findings offer practical recommendations for better understanding, monitoring and managing water age and water temperature in real operational drinking water supply systems, suggesting that biostability can be achieved through more integrated management of these factors rather than focusing solely on a single parameter, such as reducing AOC or increasing disinfectant concentrations.