Water pollution is a critical worldwide problem that significantly threatens human well-being and environmental sustainability. Conventional water treatment methods are effective for many contaminants, but they do not remove emerging pollutants or meet increasingly stringent quality standards. Nanotechnology could provide some answers thanks to the use of nanomaterials with special physicochemical properties. In this chapter, various classes of nanomaterials used for water treatment are discussed in detail, including carbon-based, metal-based, metal oxide, composite materials, etc. This chapter discuss the mechanisms of contaminants removal with these nanomaterials including adsorption, catalytic decomposition, photocatalysis, disinfection, and membrane filtration. Moreover, the chapter elaborated on the specific uses of nanomaterials for various pollutants such as organic compounds, pathogens, heavy metals, nutrients from several sources of water such as industrial wastewater, groundwater, and saline water. Furthermore, the health and environmental consequences in water treatment are reviewed using nanomaterials, and approaches for reducing possible risks are discussed along with associated regulatory aspects. The chapter concludes by addressing recommendations regarding policy and practice to promote the responsible and effective adoption of nanomaterial-based water purification technologies, followed by a discussion on technical and operational challenges, scalability, economic feasibility, and future research directions in this fastmoving area.