Operator terms · Water
What is coagulation in water treatment?
Coagulation is adding a chemical, such as alum, that neutralizes the charge on tiny suspended particles so they stop repelling each other. It is the first step in removing cloudiness from water: the particles can then clump together. Flocculation follows, gently mixing them into larger, settleable clumps.
Last reviewed 2026-08-03
Why it is needed
The particles that make water cloudy carry a like charge, so they repel and stay suspended. A coagulant cancels that charge so they can start to gather.
What comes next
Coagulation is quickly mixed in, then flocculation gently stirs the water so the particles collide and grow into floc that settles out or is filtered.
Common questions
- What chemical is used?
- Commonly alum (aluminum sulfate) or a similar coagulant.
- What does coagulation do?
- Neutralizes particle charge so suspended particles can clump together.
- What follows coagulation?
- Flocculation, then sedimentation and filtration.