Which chemical is added for pH adjustment when the raw water pH is 6.2?

• A. Lime
• B. Carbon dioxide
• C. Sodium hypochlorite
• D. Sodium hydroxide

Answer: (C)

Raising pH requires adding an alkaline chemical. When raw water pH is 6.2, you’d typically use lime (calcium hydroxide) to push the pH upward toward neutral. Lime is a common choice because it effectively increases pH and also adds alkalinity, which helps stabilize the water during treatment and supports downstream processes like coagulation.

Carbon dioxide would lower pH, so it isn’t used for pH adjustment in this case. Sodium hypochlorite is used for disinfection, not for setting pH. Sodium hydroxide could raise pH as well, but lime is the standard, cost-effective option for bulk pH adjustment and alkalinity control in many treatment plants.