The bachelor thesis explains and describes characteristics, details and how the water supply system of the town of Rijeka operates. A water supply system is defined as a communal activity that deals with the supply and distribution of water from springs to consumers. The one in Rijeka is characterized by significant underground circulation of water, which is typical of a karst area where the town of Rijeka is located. The water supply system of the town of Rijeka includes five water pumping stations: Rječina, Zvir, Zvir II, Martinšćica, Perilo, Dobra, and Dobrica. In addition, the water supply network includes areas of the cities of Rijeka, Bakar, Kraljevica and Kastav, as well as the municipalities of Kostrena, Jelenje, Viškovo and Čavle. Today, two-thirds of water is consumed by households with a total population of 200,000 and a minor part by economic activities due to the closure of numerous industrial plants. The paper also describes the high development of a complex water supply system whose data indicate a quality that is almost comparable to the European Union standards. Since Rijeka area belongs to the karst that affects its hydrogeological picture, the method of construction of the system is specific due to sensitivity to external influences and generally very small water losses in the whole system. Therefore, this paper states and explains how such a system works so that the minimum yield of the source exceeds the total consumption many times over.