The master's thesis presents the optimization in the water supply system of the small settlement of Donja Drenova with industrial area belonging to the city of Rijeka. The optimization consists of three variants in which the main goal was the gravity flow of water to consumers in order to avoid the installation of pumping stations and to install water reservoirs/water towers at different elevations and through the elaboration of the master's thesis to conclude which variant is the most cost-effective solution, as well as to determine the optimal postion of the water reservoir or water tower. The master's thesis begins by exploring the history of the Rijeka City, basic geographical, demographic and geomorphological characteristics of the settlement of Donja Drenova and the city of Rijeka are considered, as well as the calculation of relevant quantities of water for consumers. In the second part of the thesis, there is a hydraulic analysis, where the gravity flow of water to consumers is considered. Gravitational water inflow is provided for all three variants, which differ in the arrangement of the water reservoire/water, which leads to different elevations of the facility and the length of the pipeline. The hydraulic calculations waere carried out in Excel and the Urbano Hydra 11 software. The Urbano Hydra 11 was used to create all schemes, situations, longitudinal profiles of pipes, characteristic transverse profile, node assembly plans and a pipeline staking plans.