Sewage consists of various organic and inorganic materials from residential and industrial sources. Its characteristics, including physical, chemical, and biological, need to be examined before designing an efficient sewage treatment system. Physically, sewage varies in color, odor, temperature, and turbidity depending on its age. It contains 350-1200 mg/L of solids. Chemically, important parameters are pH, dissolved oxygen, biochemical oxygen demand, and chemical oxygen demand. Biologically, sewage contains various microorganisms, including pathogens, that carry out decomposition processes essential to treatment. Understanding sewage characteristics is vital for proper treatment plant design.