Water Treatment
Section: 10. Chemistry of the Environment | Syllabus: Cambridge IGCSE Chemistry (0620)
Treating the Domestic Water Supply
Water from natural sources must be treated before it is safe to drink. Three stages are used:
| Stage | What it does |
|---|---|
| Sedimentation and filtration | remove suspended solids - heavier particles settle out (sedimentation), then the water is passed through beds of sand/gravel to remove finer particles (filtration) |
| Use of carbon | removes tastes and odours from the water |
| Chlorination | kills harmful microbes, making the water safe to drink |
Worked Example
- Question: four processes are listed - 1 filtration, 2 sedimentation, 3 distillation, 4 chlorination. Which processes are used in the treatment of the domestic water supply?
- Answer: 1, 2 and 4. Sedimentation and filtration remove suspended solids, and chlorination kills microbes. Distillation is not used - it is far too energy-intensive to apply on the scale of a domestic water supply.
Common Mistakes
- ❌ Including distillation as a stage of domestic water treatment
- ✓ distillation is not part of the domestic treatment process - it is too energy-intensive for the volumes involved; the three real stages are sedimentation/filtration, use of carbon, and chlorination
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