Disinfection & Chemical Addition

Several chemicals are added to the water throughout the different processes to facilitate water treatment. They include chemicals for disinfection (chloramines), corrosion inhibition (orthophosphate), pH balance (sodium hydroxide) and dental health (fluoride). The concentrations of each of the majority of these chemicals must meet EPA standards.

Chloramine (ClNH3)

The City of Durham has been using chloramination as the method of disinfection for drinking water since January 2002. Chlorine and ammonia react chemically to produce combined chlorine or chloramine, which is an effective method for killing many types of bacteria and other germs. Using chloramination helps to reduce the formation of disinfection by-products in the water distribution system. The city maintains a running annual average concentration of 2.9 mg/L or parts per million (ppm) of chloramines in water leaving the city’s treatment plants. Learn more about the City's use of chloramines online (PDF).

Zinc Orthophosphate (ZnPO4)

The City of Durham has used zinc orthophosphate to inhibit corrosion in service lines and household plumbing since the 1970s. Phosphates create a protective coating on metal surfaces and reduce water’s chemical activity, which decreases the processes that lead to corrosion. The city currently maintains a concentration of 0.8 mg/L (ppm) of zinc orthophosphate in the water leaving the city’s treatment plants

Sodium Hydroxide (NaOH)

Balancing the acidity/alkalinity of our drinking water is a very important part of the treatment process. pH is a measure of a liquid’s acidity/alkalinity; acids have a pH below 7 and bases (alkaline substances) have a pH above 7 to 14. Stronger acids have lower pH’s and stronger bases have higher pH’s. In 2010, the pH of Durham’s water ranged from 7.3 to 7.7 (7 being neutral).

Fluoride (H2SiF6)

Fluoride in the form of hydrofluorosilicic acid has been added to Durham’s drinking water since the late 1950s in order to prevent tooth decay. According to the American Dental Association (ADA), fluoridation is a safe and effective means of preventing tooth decay. It has been cited by the Centers for Disease Control and Prevention as one of 10 great public health achievements of the 20th century. Studies show that fluoridation can prevent between 15% - 40% of decay. The ADA cites over 60 years of studies supporting this conclusion. The city maintains a fluoride concentration that ranges from 0.47 to 1.0 mg/L (ppm) in our drinking water.

Visit the American Dental Association for more information on fluoride in drinking water.