Slow sand filtration (SSF) is one of the traditional methods of water treatment yet gaining attention as a promising method. The rising demand is owing to its simplicity, environmental friendliness and effectiveness, which can reach 90-95%. This chapter reviews the principles and mechanisms underlying SSF, particularly addressing the physical, biological, and chemical processes that contribute to its effectiveness. Furthermore, the chapter delves into the design and construction of SSF systems, with a particular emphasis on the critical components and factors that facilitate the attainment of optimal performance. The efficacy of the method in enhancing water quality is assessed through a variety of analytical methods, including the removal of turbidity, the reduction of pathogens, and the removal of organic matter. The chapter also encompasses the environmental impact assessment of SSF to guarantee its long-term sustainability.