This chapter provides an in-depth overview of the global water crisis, sources of contamination, and the urgent need for sustainable purification strategies. It outlines the impacts of industrial pollutants, persistent contaminants, and PFAS on human health and ecosystems. A detailed discussion of current remediation technologies sets the foundation for understanding the limitations of conventional methods. The latter sections introduce the role of advanced materials—particularly nanomaterials—in addressing water treatment challenges through their structural versatility, tunable properties, and multifunctional performance. This chapter concludes with a critical assessment of future needs in nanomaterial development for practical water purification.