The global demand for clean and safe water is intensifying due to increasing industrialization, urban expansion, climate change, and the widespread occurrence of persistent and emerging contaminants. Conventional water treatment technologies often lack the adaptability, selectivity, and efficiency required to address the diverse and complex nature of today’s pollutants. In this context, nano-enabled polymers, advanced hybrid materials that combine nanostructured functionalities with polymeric matrices, have emerged as a new frontier in water purification. These materials exhibit high surface areas, customizable chemical functionalities, and multifunctional capabilities, allowing them to function as effective adsorbents, selective membranes, antimicrobial agents, photocatalysts, and sensors. In recent decades, substantial research has focused on the development of polymer-based nanocomposites by embedding nanoparticles or nanofillers into natural and synthetic polymer backbones such as dendrimers, cellulose, and resins. These composites exhibit superior mechanical, thermal, and physicochemical properties tailored for environmental applications. Despite significant advancements, challenges such as nanoparticle agglomeration, difficulty in material recovery, recyclability, and long-term stability remain critical barriers. Fabrication strategies, including solution blending, melt compounding, in situ polymerization, electrospinning, microwave-assisted synthesis, and selective laser sintering, are continually evolving to ensure uniform dispersion, structural integrity, and scalable production. This chapter offers an in-depth review of the synthesis, modification, and application of nano-enabled polymer systems in water purification, with a focus on their roles in removing heavy metals, organic pollutants, pathogens, and salts. It also addresses the key performance determinants, environmental safety considerations, and limitations in current technologies. Finally, it explores future directions emphasizing the development of next-generation smart nanopolymer stimuli-responsive, regenerative, and eco-friendly materials to transform the landscape of sustainable water treatment solutions.