This chapter presents the physicochemical properties of the functional nanomaterials and their problem-solving capacities in terms of both quantity and quality. Physicochemical methods such as adsorption, membrane separations, and electrochemical methods can remove pollutants from water systems. Adsorbents based on functional nanomaterials such as nanosized metal oxides, nanocomposites, graphene, carbon nanotubes, and noble nanometals have high surface area with reactive sites, impart fast kinetics, and can be tailored to have specific affinity toward targeted contaminants. The performance of these nanoadsorbents is observed to be several magnitudes higher than the conventional adsorbents. The membrane separation process enables water reclamation from unconventional sources such as municipal wastewater. Advanced oxidation processes can be categorized into photochemical and nonphotochemical processes. The photochemical process is also known as "photocatalysis" that removes trace contaminants and microbial pathogens from water. Carbon nanotubes (CNTs) are carbonaceous nanomaterials having unique physicochemical properties due to their one-dimensional structure. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA. All rights reserved.