Wastewater treatment refers to the process used to convert wastewater into an effluent (outflowing of water to a receiving body of water) that can be returned to the water cycle with minimal impact on the environment or be directly reused. The latter is called water reclamation because treated wastewater can then be used for other purposes.

The treatment process takes place in a wastewater treatment plant (WWTP), often referred to as a Water Resource Recovery Facility (WRRF) or a sewage treatment plant.

The treatment of wastewater is part of the overarching field of sanitation. Sanitation also includes the management of human waste and solid waste as well as storm water (drainage) management. By-products from wastewater treatment plants, such as screenings, grit and sewage sludge may also be treated in a wastewater treatment plant. Chlorination remains the most common form of waste water disinfection.

Chlorine is used to achieve disinfection goals by eliminating bacteria and viruses. Caustic Soda is used as a pH stabilizer, metal precipitant, and alkaline cleaner.

Ferric chloride is used to remove metal substances from the wastewater that would otherwise harm the environment and all living organisms. It is highly valued as a chemical which makes water safe to drink. In addition, Hydrochloric Acid is used to lower the pH of the wastewater.