This topic summary covers Knowledge Organiser: Water Treatment within Water Treatment for GCSE Chemistry. Revise Water Treatment in Using Resources for GCSE Chemistry with 23 exam-style questions and 15 flashcards. This topic shows up very often in GCSE exams, so students should be able to explain it clearly, not just recognise the term. It is section 14 of 14 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Knowledge Organiser: Water Treatment
Key Terms
- Potable water: Safe to drink — not the same as pure water
- Sterilisation: Killing microorganisms (e.g. by chlorination)
- Distillation: Heating to steam then condensing — removes all dissolved substances but uses lots of energy
- Desalination: Removing salt from seawater — by distillation or reverse osmosis
- Sedimentation: Particles settle under gravity in tanks
Must-Know Facts
- 4 stages: Screening → Sedimentation → Filtration → Chlorination (SSFC)
- Chlorination kills bacteria and pathogens
- Potable water ≠ pure water (still has dissolved minerals)
- Desalination is expensive due to high energy use
- Sewage treatment: Primary (physical) → Secondary (biological) → Tertiary (chemical, HT)
- Sludge from sewage treatment produces methane gas for energy
Key Equations
- No calculation equations — descriptive/process topic
- Chlorination: Cl₂ + H₂O → HCl + HClO (kills microorganisms)
- Water treatment order: Screening → Sedimentation → Filtration → Chlorination
Common Mistakes
- Saying potable water is pure water: Potable water is SAFE TO DRINK — it still contains dissolved minerals and is NOT chemically pure
- Getting the treatment stages in the wrong order: The correct order is Screening → Sedimentation → Filtration → Chlorination — mixing up filtration and sedimentation loses marks
- Saying distillation is the normal water treatment method: Distillation produces pure water but uses too much energy for everyday water supply — chlorination is used for potable water treatment
- Forgetting why desalination is limited: Desalination is not widely used because it requires very high energy input — it is only cost-effective in water-scarce regions with cheap energy
Practice questions for Water Treatment
What does the term 'potable water' mean?
Explain what happens to the sewage sludge produced during waste water treatment, and why this process is useful.
Quick recall flashcards
Name two ways to conserve water at home
Low-flow taps/showers, dual-flush toilets, fix leaks, rainwater harvesting
What is potable water?
Water that is safe to drink (low levels of dissolved salts and microbes)