Water losses are responsible for increased energy consumption in water supply systems (WSS). The energy associated with water losses (EWL) is typically considered to be proportional to the water loss percentage obtained in water balances. However, this hypothesis is yet to be proved since flow does not vary linearly with headlosses in WSS. The aim of this paper is to validate the hypothesis, present real-life values for water-energy balance (WEB) components, and reference values for the key performance indicator that represents the ratio of total energy in excess (E3). This validation is achieved through the application of two approaches—top-down and bottom-up. The first approach requires minimum data, gives an overview of the main WEB components, and provides an effective diagnosis of energy inefficiencies through the calculation of E3 related to pumps, water losses, and networks. The second approach requires calibrated hydraulic models and provides a detailed assessment of the WEB components. Results allow the validation of the stated hypothesis as well as show that the most significant energy inefficiencies are associated with surplus energy, pumping, and water losses, each reaching up to 40% of total input energy. Less significant components are pipe friction and valve headlosses, each reaching up to 15% of total input energy.
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