The Water Treatment Division is responsible for raw water supply, treatment, and pumping to the distribution system. The Division maintains a staff of certified water treatment operators. The Division also oversees twenty-three wells on the groundwater system. Maintenance of the elevated tanks is the responsibility of the Water Treatment Division. The Division handles and responds to water quality complaints.

The City of Wilmington operates a 25 million gallon per day water treatment plant withdrawing water from the Cape Fear River. Raw water from the river is pumped to the plant to eliminate the intake of salty water during tidal changes.

The plant operation is a combination of conventional treatment and upflow clarification with ozonation as the primary disinfection method followed by filtration and chlorine disinfection, fluoridation, corrosion control, and pH adjustment. The Sweeney Water Plant receives raw water from the Cape Fear River directly into the ozone contactor where ozone is applied. Upon leaving the contactor, the raw water is then split at the desired rate to either the North Plant or the South Plant.