In last years all countries of the European Union experience decrease of water consumption. What is worse, in most cases large European water treatment plants (WTP) have been design and built decades ago, when water consumption was much higher than nowadays. It is a challenging task to adjust WTP’s capacity to the current water demand as it is associated with costs and safety issues. Minding that fact, authors decided to propose an new authorial methodology of combined reliability-cost efficiency assessment for water supply system with exceeded redundant capacity, based on new index - unit indicator of reliability-cost efficiency. It included both reliability and costs aspects. It was decided to present the new method on example of the pumping subsystems working for WTP in Poland. The research was based on Activity-Based Life Cycle Costs (AB-LCC) methodology together with two-parametric reliability evaluation. Using real operational and financial data an application of proposed authorial reliability-cost indicator was presented. The reliability-cost efficiency assessment allowed to present how operation of each pumping subsystem influenced global operational costs of WTP. This information is essential for decision-making process for rational management of technical facilities.
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