The need for a common international terminology is growing the last few years regarding the performance evaluation of urban water distribution systems, due to the wide diversity of definitions used across the word (even within the same country). Thus, the IWA Task Forces on Water Losses developed an international standard approach to calculate the water balance of an water distribution system utilizing best practices around the world. In Greece the need for a common approach is even more urgent as the country faces severe water shortage problems and there is no place for water losses due to ignorance. Greek Water Utilities are far behind in applying appropriate indicators to safely calculate the water losses level and therefore design effective strategies to reduce it. The paper presents the results of the Kos Town (Kos island) project regarding the performance evaluation of its water network. The project’s goals were to develop the system’s water balance (based on the IWA guidelines), calculate several performance indicators and compare them to national and international relative data available. The final outputs were to: a) estimate the apparent and real losses levels; b) calculate the non-revenue water level and its cost; and c) provide solid proposals targeted to an effective water losses reduction policy. The difficulties faced during the whole attempt are also presented.