In the recent time, nanotechnology has emerged as one of the most important disciplines of science and technology. Particularly, the synthesis of microbe-based nanomaterials, often referred as “green synthesis,” substantially reduces the utilization of hazardous chemicals, hence, offering an eco-friendly, economical, energy-efficient bio-based manufacturing process. Microorganisms such as bacteria, actinomycetes, fungi, viruses, and algae are most commonly used for the synthesis of microbe-based nanomaterials. The availability of drinking water is declining severely worldwide; therefore, there is an urgent need to develop effective water purification technologies to ensure availability of safe water for human consumption. Several traditional methods for water purification are being used from past few decades. Recently, nanotechnology displays a promising smart solution for water purification processes. This chapter describes the efficacy of various nanomaterials especially focusing on microbial nanoparticles and filter membranes in water treatment technologies. The microbial nanoparticles are effective in eliminating contaminants from water and could open up innovative possibilities in water purification processes.