Water pollution is one of the most important global challenges and requires innovative and efficient purification technologies. Carbon-based nanocomposites have emerged as promising materials because of their excellent physicochemical properties, including high surface area, chemical stability, tunable functionalities, and superior adsorptive and catalytic capabilities. This chapter covers the application of different graphene, carbon nanotubes (CNTs), and carbon nitrides in advanced water purification techniques such as adsorption, photocatalysis, membrane filtration, and electrochemical processes. Hybrid nanocomposites combining metal oxides, polymers, and antimicrobial agents allow for an enhancement in the contaminant removal efficiency of multifunctional water treatment. Challenging discussions related to sustainable synthesis, mass production, and environmental impact are given below. Research on scalability and cost-effective solutions and frameworks of regulatory oversight to ensure safe deployment have been the main foci in future work.