Rainwater Harvesting system (RWHs) can be considered as an alternative water resource in the era of the climate crisis. This research aims to study the effectiveness of a RWHs for domestic non-potable use and the water demand of the community in a Mediterranean site (Chios island, Greece). A water balance model is applied to simulate the behavior of a rainwater tank and calculate the daily water savings. The analysis correlates rainwater tank capacity, catchment area and population. The operation of the rainwater collection system has been calculated for seven years. In order to assess the investment risk regarding the application of the RWHs, the financial ratio of PayBack (PB) period was determined. The multifaceted character of Rainwater Harvesting (RWH) practice in the three-dimensional concept of sustainability is discussed. This study concludes that RWH contributes to the greening of society, dealing with water scarcity in urban areas.