Recent changes in European Union legislation impose new obligations on water utilities to gather, analyse, and report impartial Key Performance Indicators (KPIs). These include data on water leakage, entity condition, energy consumption, and its sources. Benchmarking has emerged as a valuable tool for collecting standardized and reliable data, facilitating improvements. Utilities in Poland participate in both national benchmarking, led by the Chamber of Commerce’s “Polish Waterworks” (IGWP), and international benchmarking through the European Benchmarking Cooperation (EBC). However, differences in data definitions affect the comparability of indicators and the accuracy of ranking results. A crucial issue is to select the most appropriate and objective KPI for water loss. The DWD mandates the use of the Infrastructure Leakage Index (ILI), but this indicator is difficult to calculate and verify, prompting a search for simpler, standardized alternatives, such as Non-Revenue Water (NRW). The authors compare selected KPIs from the two benchmarking projects, EBC and IGWP, showing that minor definitional differences may make the comparison non-objective or impossible.