In the pH range 6-9, dissolved inorganic carbon should be greater than how many mg/L?

• A. 2.5 mg/L
• B. 2 mg/L
• C. 3.5 mg/L
• D. 5 mg/L

Answer: (B)

In this pH range, dissolved inorganic carbon provides the buffering that helps keep water’s pH stable and supports corrosion control. Bicarbonate is the dominant inorganic carbon species around pH 6–9, so the DIC level largely reflects buffering capacity. Maintaining DIC above about 2 mg/L gives enough buffering to resist pH shifts and maintain alkalinity, which is important for protecting the distribution system from corrosion and for effective disinfection. Values at or just above 2 mg/L meet the minimum requirement, while higher values exceed the minimum buffering needed.