Nanocomposites such as metals, metal oxides, carbon-based polymer membranes, and metal–organic framework (MOF) hybrid composites have shown great promise in improving wastewater treatment due to their advanced properties and ability to effectively remove contaminants. However, their environmental impact and sustainability are important considerations as these materials become more widely used. This chapter examines the potential environmental risks associated with nanocomposites, including the release of nanoparticles into ecosystems, their persistence, and their possible effects on human health and the environment. It also addresses the challenges related to their recycling, disposal, and long-term degradation. In terms of sustainability, the chapter explores energy-efficient production methods, the use of renewable materials, and the potential for green synthesis approaches to minimize environmental harm. Future perspectives focus on the development of biodegradable and eco-friendly nanocomposites, along with strategies for improving their recyclability and reducing their ecological footprint, ensuring that these materials can be both effective in water treatment and sustainable in the long term.