The theme of this graduate thesis is a statistical analysis of water supply system of the town of Valpovo and the suburban settlements, of the municipality of Petrijevci, of the municipality of Bizovac, and of the municipality of Koška with the settlements which belong to the named municipalities. The thesis puts an emphasis on the analysis of water supply system failures. The tracking of the failures and the preventive interventions which are performed in order to reduce losses in water supply system to a great extent ease the implementation of new technologies such as GIS or NUS which track and analyse the failures, and the application of IWA technology for loss budget calculation. The graduate thesis shows frequency of failures of certain kinds of built-in pipes depending on the material type that they are made of as well as the age of water pipes. The influence of the material type, the age, and particularly the quality of maintenance of water supply system, on the appearance of water losses were processed and analysed in order to bring the above mentioned to the economically profitable level. The analysed and processed data was collected from 2011 to 2018. The data was collected for the entire water supply system of the public supplier of water services of water supply system of the town of Valpovo, of the municipality of Petrijevci, Bizovac, and of the municipality of Koška with the belonging settlements, and the smaller part of the town of Belišće (2 streets). The stated area is supplied from two sources, respectively from two water intakes. The complete area of the municipality of Petrijevci, the municipality of Bizovac, the suburban settlements of Valpovo, as well as a smaller part of the town of Valpovo are supplied with water from the water well Jarčevac. The rest of the town of Valpovo, and the the suburban settlement of Nard, and the observed smaller part of the town of Belišće are supplied with water from Belišće water intake. Considering the fact that the theme of this thesis is the statistical analysis of the work of the communal water structures and the analysis of losses, it is important to mention that on the water supply area there are 6.937 users with a built-in water counters out of which 6.270 are physical users and 667 are legal entities. On the water supply area, 978 hydrants were installed which cause losses due to unauthorised use. The water losses of the water supply network system can be due to failures, because of an inaccurate measuring of the water counter, unauthorised use, etc. This thesis processed the losses regardless their cause of appearance.