Water pollution is still considered one of the biggest problems in the modern world, and methods of treating it have been consistently developed to meet the rising need for clean water. The fabrication of efficient and selective natural or synthetic catalysts, membranes, and adsorbents has been the subject of extensive research during the past few decades. The exploration of synthesizing nontoxic, biocompatible, affordable, and effective nanocomposite materials continues through the usage of nanofillers which provide a larger interfacial surface area to the nanocomposite materials. Nanofiller can be seen as a significant potential filling material that enhances the physical and mechanical performance of the synthesized nanocomposites. The larger specific surface areas of fillers with nanoscale dimensions can be up to or more than 1000 m2/g. Nanofillers can considerably enhance the thermal, tribological, and mechanical properties of polymer composites. In addition to having a high surface-to-volume ratio for loading biomolecules like enzymes, chitosan, cellulose, etc., nanocomposites also have great mechanical strength, high catalytic activity, electrical conductivity, and high redox reactivity. Thus, suitable nanofiller can be employed to enhance the performance of different nanocomposite materials in numerous ways. The current chapter provides information on the types and properties of nanofillers, nanofiller-based natural or synthetic polymer composites, the use of nanofillers in synthesizing polymeric composites to improve their mechanical (tribological, impact, flexural and tensile) properties, and, most significantly, their uses in the wastewater remediation industry. Furthermore, this chapter discussed various ways that can be used to synthesize and characterized polymeric nanocomposites, among which the most prevalent procedures are selective laser sintering, mixing, microwave-assisted, electrospinning, in situ polymerization, and melt-mixing. The chapter also discusses the application of different polymeric nanocomposites for wastewater treatment, as well as the key factors that affect their effectiveness, and it identifies challenges and future research outlooks.