Water scarcity problems and the need for reduced consumption of fossil fuels lead to the transition to renewable energy sources (RES). The proper management of RES is the key issue, especially in small not interconnected islands. In this research work a Hybrid Renewable Energy System (HRES) on a small island in the Aegean Sea is evaluated for ten years of hydrometeorological data. The objective is the production and storage of the required energy for the electricity needs of the area, as well as, for the desalination of seawater for domestic and irrigation water fulfillment. Results concerning the reliability of the system, the fulfillment of water and energy demands and the loss of load expectation are presented. The simulations will give valuable information about the produced and stored energy, its controlled distribution for the water and energy demands of the island and HRES’s potential in these demands of the local society over one decade.