What is filtration?

• A. Adding chlorine to inactivate microbes
• B. Heating water to evaporate contaminants
• C. Coagulating with alum to form flocs
• D. Removing remaining particles by passing water through filter media

Answer: (D)

Filtration is the process of removing remaining particles by forcing water to pass through a filter medium (like sand, gravel, activated carbon, or a membrane). As water moves through the media, solid particles and some micro‑organisms are trapped, making the water clearer and reducing turbidity. This step typically follows coagulation/flocculation and sedimentation in a treatment train, and backwashing helps clean the media so it can continue to trap particles.

The other activities are different treatment steps: adding chlorine inactivates microbes (disinfection); heating water to evaporate contaminants is distillation (a separation method); coagulating with alum forms flocs to settle out solids (coagulation/flocculation), not filtration.