Water pollution poses a major threat to human health, ecosystems, and sustainable development, creating an urgent need for advanced and environmentally friendly treatment technologies. Nanotechnology has emerged as a highly effective solution by utilizing engineered nanomaterials with exceptional physicochemical properties, including high surface area, superior catalytic activity, antimicrobial behavior, and enhanced adsorption capacity. This review examines the role of nanotechnology in water purification through the application of nanoparticles, nanocomposites, nanomembranes, nanocatalysts, and nanosensors for the efficient removal of heavy metals, pathogenic microorganisms, pesticides, pharmaceutical residues, and other emerging contaminants. Particular emphasis is placed on iron oxide nanoparticles, titanium dioxide, silver nanoparticles, carbon based nanomaterials, and zero valent iron due to their outstanding remediation performance. Green synthesis approaches for nanomaterials are highlighted as sustainable alternatives that reduce environmental impacts while maintaining treatment efficiency. The review also discusses the significant potential of nanotechnology for arsenic removal from groundwater, especially in arsenic affected regions such as the Indo Gangetic Plain. Furthermore, nanotechnology supports real time water quality monitoring and the development of decentralized, low maintenance water treatment systems. Although challenges related to nanoparticle toxicity, environmental fate, economic feasibility, and large scale implementation remain, continued interdisciplinary research and responsible material design can accelerate the safe adoption of nanotechnology for next generation, sustainable water purification systems. Nanotechnology Water Purification Nanomaterials Arsenic Removal Sustainable Water Treatment. 1046-1051 Issue-6 Volume-9 Akbare Azam