Investigating innovative methods for effective water and wastewater treatment has become necessary in order to solve global environmental concerns, such as pollution and water scarcity. Customising nanoparticles and nanocomposites made especially for water purification purposes is one way that nanotechnology offers potential prospects. This study explores the latest developments in nanoparticle-based water treatment technologies, emphasising their inherent qualities, synthesis processes, and range of uses. For the purpose of removing pollutants from water and wastewater matrices, a variety of nanoparticles, including metal nanoparticles and carbon-based nanomaterials, as well as hybrid nanocomposites, including metal/metal oxide-based nanocomposites and polymer-based nanocomposites, were highlighted. Moreover, this chapter clarifies the fundamental principles guiding the methods of pollution removal that are made possible by nanoparticles, including adsorption, catalysis, and membrane filtration for environmental sustainability. Moreover, it delves into the environmental consequences and difficulties linked to the extensive implementation of water treatment methods based on nanoparticles. By integrating earlier research findings, this study provides significant new information on various nanoparticles and composites to mitigate water-related issues. Transferring nanomaterial-based therapy solutions to larger-scale systems poses considerable obstacles, even with encouraging outcomes in the laboratory. To increase the effectiveness of wastewater treatment, research should focus on developing nanomaterials with enhanced selectivity towards target pollutants while minimising interference from other chemicals.