Processes used to reduce or eliminate wastewater pollutants from before they are discharged.Pre-treatment helps in producing high quality water by removing unwanted impurities from the product water before combining it with the primary water supply in order to recover some of the contaminants. Most untreated water usually are drained from households into a aggregate line of underground pipelines that are delivered to large-scale wastewater treatment plants that carry out the pretreatment.