Access to clean and reliable water sources is becoming increasingly difficult in many parts of the world. Industrial activity, growing populations, and climate-related disruptions are putting significant stress on available water supplies. These pressures have encouraged the development and use of more advanced technologies for treating both drinking water and wastewater. In recent years, a number of promising solutions have gained attention, including technologies such as membrane bioreactors, reverse osmosis systems, advanced oxidation methods, electrocoagulation setups, granular activated carbon filters, zero liquid discharge approaches, and bioelectrochemical treatments. While each of these technologies has demonstrated success in specific applications, they differ considerably in terms of operating conditions, efficiency, and resource demands. Because of the variety and complexity involved, identifying the most appropriate method for a specific application presents a substantial challenge. Decision makers often have to balance technical performance with environmental impact, cost, and other practical concerns. In light of this, methods that allow for the structured comparison of multiple alternatives—particularly multi-criteria decision-making (MCDM) approaches—can offer valuable guidance. This study proposes to examine and compare several of the most recognized sustainable water treatment technologies using a decision-making framework. Rather than relying on just one metric, the evaluation will consider a range of factors that are relevant in real-world settings, including both qualitative and quantitative elements. The outcomes of this analysis are intended to support more informed and context-sensitive decisions in water treatment planning, especially in environments where sustainability is an increasingly critical concern.