Which sequence correctly lists the typical steps in conventional drinking water treatment?

• A. Coagulation/Flocculation, Sedimentation, Filtration, Disinfection, and Adjustment of pH/Alkalinity.
• B. Filtration, Coagulation/Flocculation, Sedimentation, Disinfection, Storage.
• C. Sedimentation, Disinfection, Filtration, Coagulation/Flocculation, pH adjustment.
• D. Disinfection, Filtration, Coagulation/Flocculation, Sedimentation.

Answer: (A)

In conventional drinking water treatment, the process follows a logical progression from removing larger contaminants to preparing water for safe distribution. Coagulation and flocculation come first because adding coagulants neutralizes the negative charges on tiny particles, allowing them to clump into larger flakes (flocs) that are easier to remove. Next, sedimentation lets those flocs settle out by gravity, reducing turbidity before water moves to the next step. Filtration then catches remaining fine particles and many microorganisms that didn’t settle, using media such as sand and aquifer-like beds to polish the water. After particulates are removed, disinfection is applied to inactivate remaining pathogens, ensuring the water is safe as it enters the supply system. Finally, adjusting pH and alkalinity helps maintain a stable water chemistry, improves the effectiveness and longevity of the disinfectant, and reduces corrosion potential in the distribution system.

This sequence is preferred because each step prepares the water for the next: coagulation creates flocs that settle, filtration removes what remains, disinfection is most effective on clearer water, and pH adjustment optimizes overall water stability and safety. If steps were rearranged—for example, filtering before coagulation or disinfecting before filtration—the treatment would be less effective, with poorer removal of particles, diminished disinfection, and greater corrosion or stability issues in the distribution system.