Describe how drinking water is made safe for human consumption from a source such as a river.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Model answer (4 marks)
Sedimentation allows large particles to settle out of the water.
Filtration through sand (and gravel) removes smaller or finer suspended particles.
Chlorination adds chlorine to the water, which kills microorganisms and bacteria, making the water safe to drink.
Filtration through sand (and gravel) removes smaller or finer suspended particles.
Chlorination adds chlorine to the water, which kills microorganisms and bacteria, making the water safe to drink.
Examiner tips
- Use the exact terms: sedimentation, filtration, chlorination. Explain the purpose of each step. Keep the answer concise – 4 marks, so one sentence per step.
- common_mistakes
- :
- Mixing up the order of steps. Using vague phrases like "cleaning" instead of specific processes.
Mark scheme (4 marks)
- Sedimentation / allow large particles to settle (out)
- Filtration through sand (and gravel) to remove smaller/finer particles
- Chlorination / chlorine is added to kill microorganisms / bacteria
- Purpose of one step clearly linked — e.g. chlorine kills microorganisms / bacteria (to make it safe to drink) OR filtration removes fine/suspended particles
Related
- All Cambridge International IGCSE Chemistry (0620) revision notes →
- How to answer a "Describe" question →
- Decode the mark scheme abbreviations →
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