Lignin, a complex and abundant renewable biopolymer derived from plant cell walls, has garnered significant interest for its versatile industrial applications. Among its many potential uses, it shows great promise in water treatment processes. Its renewable nature makes lignin a sustainable resource for industries. This chapter examines the special qualities of lignin, such as its biodegradability, natural abundance, and functional groups that facilitate interactions with waterborne pollutants and suspended particles that make it a viable option for flocculation. The mechanics of lignin-based flocculation are explained, emphasizing how it can cause pollutants to clump together and form larger clusters that are easier to remove from water systems. The chapter also covers the various techniques for lignin extraction from biomass sources and structural optimization to improve flocculation efficiency. The usefulness of lignin as a flocculant in drinking water purification, industrial effluent remediation, and wastewater treatment is illustrated through case studies and experimental data. The use of lignin-based flocculants has several benefits for the environment and economy, including their cost-effectiveness and biocompatibility. The challenges and potential advantages of utilizing lignin as a sustainable alternative to conventional flocculants are explored, emphasizing the need for further research and technological advancements to fully optimize its application in water treatment processes. This chapter offers in-depth insights into harnessing lignin’s natural properties as a flocculant for sustainable and eco-friendly water treatment solutions. It highlights lignin’s potential to enhance environmental restoration efforts and contribute to sustainable resource preservation. By focusing on lignin’s role in water treatment, the chapter underscores its importance in advancing green technologies for a cleaner environment.