Method of safety analysis of water supply system

In the paper the method of reliability and safety theory application in water supply system (WSS) operation is presented. Among all, grounds of global assessment of water supply system were defined in the form of measurable reliability parameters. The parameters characterize both technical and technological efficiency of lifetime of individual elements that build water production subsystem (WPS) and water distribution subsystem (WDS). Moreover, they are related to safety analysis of their working. Application aspects as well as theoretical aspects of presented subject matter are intensively studied in the area of scientific research and municipal service. The proposed methodology of safety analysis is based on assumption that WSS is in one of reliability exploitation states (i.e. full safety, acceptable safety menace, controlled safety menace, and safety loss) which were defined on the basis of studies that have been conducted in Poland in many years. These states are characterized by different safety levels which follow from production capacity of WPS, failure frequency on water mains, water quality changes in WDS considered as THM concentration in transported water. One of essential parts of the paper is the probabilistic model of water quality changes in distribution subsystem. These changes cause different quality states of the system so their identification is important for the safety management with respect to the minimization of water consumer health risk. The probability that the system is in given safety state in the arbitrarily chosen moment is calculated. Presented method is applied to the data from the real WSS in Wroclaw (Poland) as well obtained results are discussed. They emphasize not only scientific significance of the method but also its useful virtues as the decision tool in the process of preparation of water companies' development strategies and Water Safety Plans.