Raw water is pumped from either Toisnot Lake or Wiggins Mill Reservoir to the treatment facilities. When raw water enters the facility, ferric sulfate reacts with natural alkalinity, or added lime, or sodium hydroxide to cause small particles to cling to one another after strong mixing. Powder activated carbon is added to control taste and odor causing substances that occur naturally in the raw water. The Wiggins Mill Plant has a system to remove solids from the basins called a trac vac system. Tube settlers are also utilized to improve settling efficiency. The water is then mixed slowly and polymer is added. The particles are then much larger. The water then enters settling basins where the heavy particles settle.
Chlorine and sodium hydroxide (pH adjustment) are added to improve mineral removal in the filters. The water is then filtered through sand and anthracite to remove remaining fine particles. Chlorine is added to kill harmful bacteria, protozoans and viruses. Lime or sodium hydroxide and a corrosion inhibitor are added to maintain pH and minimize potential for corrosion in City distribution lines and household plumbing. Fluoride is then added to aid in the prevention of tooth decay.
In order to ensure that tap water is safe to drink, the EPA prescribes regulations which limit the amount of certain contaminants in water provided by public water systems. Over 300,000 routine tests are performed on the water each year. The City of Wilson's drinking water supply meets all federal and state water quality requirements.