What is the primary purpose of municipal water treatment, and what roles do coagulation, flocculation, filtration, and disinfection play?

• A. To heat water to boiling
• B. To remove contaminants and pathogens; coagulation forms flocs; flocculation aggregates; filtration removes solids; disinfection kills microbes
• C. To increase mineral content in water
• D. To measure water pH

Answer: (B)

Municipal water treatment aims to remove contaminants and pathogens to make water safe for people to drink. In this sequence, coagulation involves adding chemicals that neutralize the charges on tiny particles, allowing them to come together into small clumps. Flocculation then uses gentle mixing to encourage those clumps to collide and grow into larger aggregates called flocs. Filtration passes the water through beds of sand, gravel, or other materials to trap remaining solids and microorganisms. Disinfection finally introduces agents like chlorine to kill or inactivate microbes, ensuring the water is microbiologically safe before it’s distributed.

Other options don’t fit the purpose: heating to boiling isn’t how a city’s treatment plant operates on an ongoing basis; increasing mineral content isn’t the goal of treatment; measuring pH is important for process control but doesn’t describe the primary purpose.