The aim of this thesis is to point out the problem of losses of drinking water from the water supply network and to show how the application of research, various mathematical analyses, measuring equipment and modern methodologies can improve the state of the water supply system. The introductory part of the paper describes the characteristics of water and its importance for society, the spatial distribution of water resources, the basic elements of water supply systems and their development throughout history and specifically the structure and managment of Vodovod d.o.o. Slavonski Brod as a public provider of water services in the wider area of the city Slavonski Brod. The next part of the paper includes a systematic analysis of the Slavonski Brod water supply system. In this part are described the types of losses, their negative impacts, obstacles to the sustainability of the system and the methods by which they can be detected. Using the IWA methodology, a standardized water balance was created in which its basic elements are explained and calculated on the basis of the collected data, with the application of reliability limits. Based on the water balance, a calculation of system performance indicators was made which was used to determine the possible extent of water loss reduction. In the last part of the paper are listed and described the proposals for improvement of the situation in the water supply system. The proposals include meeting the preconditions for the implementation of modern methods for reducing water losses, including the calculation of economic level of leakage, the development of a geographic information system and the development of a hydraulic network model. Finally, the methods of implementing DMA and PMA zones are explained in general and on the concrete example of the Slavonski Brod water supply system, ie how significant savings can be achieved trough the control of flow and pressure by the sectorization of the water network into discrete metered areas and pressure managment areas.