The Evolution of Unconventional Water Resources in the Hellenic World

The water demand is increasing across all sectors, driven by intensive agriculture, overexploitation and urbanization, tourism, and industrial development. This trend is set to intensify in the context of climate variability, with an anticipated rise in the frequency and intensity of prolonged dry periods. As a result, conventional water resources, including surface and groundwater, are facing significant pressure and cannot meet the growing water needs. In contrast, unconventional (UWR) or non-conventional water resources, such as treated wastewater, salinized water, and rainwater harvesting are emerging as valuable and strategic resources and will play a pivotal role in the new era. Therefore, it is evident that the management of water resources must also include UWR to address the issue of water scarcity, with the ultimate goal of achieving a sustainable water future. This review aims to provide an overview of the currently and potentially available UWR in Greece. In addition to current trends and prospects, this study examines the utilization of unconventional resources in ancient Greek civilizations. The main conclusion is that in the context of the circular economy and the implementation of the Sustainable Development Goals (SDGs), the use of unconventional water resources is crucial for facing the problems that are emerging.