Microbiological safety of water in the risk management of operating water supply systems – a case study of Silesia, Poland

According to Directive 2020/2184, each water supplier is required to develop a water supply risk management system, such as the World Health Organization’s recommended Water Safety Plan, implement it and apply it to daily water supply practices. An important element of risk management in water supply systems (WSS) is to ensure the supply of water that is healthy and clean, that is, free of all microorganisms and parasites and any substances in quantities or concentrations that pose a potential danger to human health. Ensuring the microbiological safety of water, while minimizing the risks associated with disinfection by-products, is particularly important in extensive WSS, where water can take days to transport, and where hydraulic parameters and sediments deposited in water supply networks favor the growth of microorganisms. This paper proposes an analytical method to support the determination of areas sensitive to the loss of microbiological safety of water, while using the model to optimize the dose of disinfectant at water treatment plants and water chlorination points in the distribution subsystem. The developed methodology is part of a review of operating procedures, especially with regard to minimizing the risk of secondary microbiological contamination of water. The research model took into account the chemical as well as microbiological variability of water quality, its age, and the operational data of the WSS operation collected by the Geographic Information System (location of water quality monitoring points, spatial location of water supply infrastructure facilities), as well as the size of the population potentially exposed to water of uncertain microbiological quality. The result of the analyses is a spatial interpretation of the loss of microbiological safety of water presented in the form of risk maps.