In performing a jar test, which factor is least important?

• A. Turbidity
• B. Color
• C. Temperature
• D. Chloride concentration

Answer: (D)

In a jar test, you’re evaluating how well a coagulant can destabilize and remove suspended solids and color-causing substances, so the main measurements you look at are how turbidity and color change after mixing and settling. Turbidity directly reflects the amount of particulate matter being removed, so it guides the recommended coagulant dose and settling effectiveness. Color helps indicate the removal of color-forming organics, which can also be affected by coagulation and flocculation, so it’s a useful indication of performance beyond just turbidity. Temperature matters because it influences reaction rates and floc formation; tests are often done at the actual water temperature to approximate plant conditions and adjust expectations accordingly. Chloride concentration, however, doesn’t play a direct role in the coagulation process or in forming flocs during a jar test, so it doesn’t inform the dosing or mixing decisions the way turbidity, color, or temperature do.