Hazardous event analysis of microbiological contamination in risk management of large water supply systems

Effective risk management in water supply systems (WSS) is based on implementation of reasonable protective barriers for reducing frequency of hazardous events and/or minimizing their impact. Loss of biological and chemical stability of water contributes to secondary water contamination in WSS that determines safety of water consumers. Factors which affect secondary water contamination may also lead to growth of biofilm, these include: the quality of water entering the distribution network (its physicochemical composition), pipeline material and age, hydraulic conditions as well as the concentration of disinfectant in the tap water. Control of these aspects is important for ensuring biological stability of drinking water. However, under dynamic conditions of WSSs operation, it is difficult to include an effect of collective evaluation of those factors on formation of reasonable protective barriers in risk management procedures. Water stagnation and pipelines’ age may affect the physicochemical water quality, which often results in biofilm growth. Therefore, the aim of this study is to identify hazardous events, which need to be considered during a risk assessment of secondary microbiological contamination of water. This paper presents an analysis of how the age of drinking water transported to the consumer and the age of pipelines affect the loss of microbiological stability of water.