<p>The increasing scarcity of fresh water all over the world has made the need for sustainable options like greywater reuse more important than ever. This study offers an extensive review of sustainable greywater management systems, with significant focus on cost–benefit analysis as a fundamental evaluative paradigm. A bibliometric Analysis of global research from 2005 to 2025 reveals the swift growth of this subject and the shift towards decentralized, hybrid, and AI-enhanced therapeutic solutions. The report sorts treatment methods into physical, chemical, physicochemical, biological, hybrid, and advanced systems. It looks at how well they work, how much they cost, and how beneficial they are for the environment. Comparative assessments of essential financial metrics like CAPEX, OPEX, payback period, and cost-benefit ratio indicate that decentralized and hybrid systems provide enhanced cost efficiency and enduring sustainability. Combining cost-benefit analysis with bibliometric and technological evaluations improves decision-making, aids in the creation of policies based on evidence, and makes it easier to employ greywater reuse on a broad scale as part of a circular economy and climate-resilient water management plan.</p>