In this thesis, a calculation and analysis of the cost-effectiveness of installing a water reservoir in a small water supply system was carried out. The water supply system is described and the water supply systems throughout history are presented. With the given input parameters, two hydrodynamic calculations were performed for a small water supply system: with and without a reservoir. Using the Pipeline program and the Hardy-Cross method, the volume flow rates in the pipes, the pressures in the pipeline nodes and the electricity consumption of the water supply system were calculated. The purpose of the installation of the reservoir was explained and one type of water reservoir was selected together with the calculation and comparison. A risk analysis was carried out and the profitability of the construction of the entire system and the water reservoir was examined. It was concluded that the water reservoir is a good way to keep the pressure constant and that it provides sufficient accumulation to maintain the operation of the system in the event of a failure. Furthermore, the project is more economically viable with the construction of the water reservoir than without it, as the electricity savings over the years are sufficient to cover the cost of building the water reservoir and the profit remains.