Reviewing Applied Methods and Strategies for Sustainable Potable Water Reuse in Water-Scarce Regions

Population growth, climate change, pollution, and prolonged droughts are contributing to increasing water scarcity, which poses a significant challenge to global sustainable water management. Among the available adaptation strategies, potable water reuse has emerged as a viable and increasingly adopted solution in areas facing water stress. This review examines evolution, regulatory frameworks, treatment technologies, and implementation strategies related to drinking water reuse worldwide. Through the historical review, it becomes clear that the idea of water reuse has deep roots (5000 years ago), while the analysis of modern legislative and intergovernmental approaches led to the conclusion that the rules governing water reuse vary depending on the country and are in most cases quite strict (e.g., the Urban Wastewater Treatment Directive (UWWTD) and the Water Framework Directive). To make potable water reuse possible, including direct and indirect systems, advanced wastewater treatment technologies are applied, among which membrane processes and advanced oxidation processes (AOPs) are most often chosen, while treatment trains are almost always used. The recent studies of potable water reuse presented highlight the interest of both the scientific community and the state. The economic review demonstrates that potable water reuse can be economically viable and more economical than other solutions, e.g., desalination. The review identifies the key challenges (technical, economic, institutional, and social) and opportunities for scaling up potable water reuse as a primary water supply option and discusses its potential role in enhancing long-term sustainable water management, especially in areas that are either arid or semi-arid.