Due to high surface area, reactivity, and tunable surface functionalities, nanomaterials (NMs) are important materials for water purification. In this chapter, the synthesis and application of NMs for water purification have been used. The mechanisms of adsorption, such as surface complexation, ion exchange, and van der Waals interactions, emphasizing their role in achieving high removal efficiencies have been discussed. The chapter divides nano-based adsorbents according to their composition, including metal-based (e.g., nanoparticles of iron oxide, silver), carbon-based (e.g., graphene oxide and carbon nanotubes), and polymer-based NMs. Challenges such as cost, regeneration, and environmental impact are discussed alongside emerging trends in functionalization techniques to enhance specificity and reusability.