Domestic water treatment: give each stage its job
Connect solid removal, carbon treatment and chlorination with different problems in the water supply.
Core and Extended · Chemistry 0620, 2026–2028. Interpret supplied or supervised evidence; a school chemical test is not a drinking-water safety assessment.
Before you begin
- Distinguish suspended solids, dissolved substances and microbes.
- Explain filtration as separation rather than automatic destruction of all organisms.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
Which observation concerns suspended-solid removal most directly?
What you will learn
- Describe sedimentation, filtration, carbon treatment and chlorination in the required domestic-supply model.
- Explain why removing visible solids, tastes or odours is different from killing microbes.
Remove solids before confusing them with dissolved contents
Sedimentation allows suitable suspended solids to settle, and filtration separates remaining solid particles using the chosen filter system. In the syllabus treatment model these stages remove solids. A classroom filter's clear filtrate does not prove all dissolved salts or microbes are absent; particle removal and complete chemical purification are different claims.
Domestic treatment uses a sequence of processes because the starting water can contain several kinds of unwanted material. In the schematic flow, solid removal is followed by carbon treatment and chlorination. Real treatment trains depend on the source and system; the diagram organises the required stage purposes rather than giving a household method or a complete water-plant design.
Carbon and chlorine answer different questions
Carbon is used to remove tastes and odours. Activated carbon has a large surface on which suitable compounds can adsorb: adsorption means attachment at a surface. That helps distinguish its role from sedimentation of large particles and from claiming carbon converts every dissolved salt into harmless material.
Chlorination kills microbes in the required treatment description. The fact that a sample has no unpleasant odour or visible sediment does not establish that this disinfection purpose is unnecessary. Name the target of each stage: solids, tastes/odours and microbes. These course explanations interpret treatment roles; they are not directions for dosing disinfectant or making unknown water safe to drink.
Pause and explain
What is carbon's required treatment role?
Worked example
A supplied water treatment route uses settling, filtration, carbon and chlorination. Explain the different targets.
Show the worked solution
- Settling and filtration remove suitable solids.
- Carbon removes tastes and odours through its treatment role.
- Chlorination kills microbes; a clear or better-smelling sample alone does not establish that target was addressed.
Answer Sedimentation/filtration: solids. Carbon: tastes and odours. Chlorination: microbes.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Explain sedimentation and filtration in the treatment route.
Give me a hint
Both target solids, through different physical separation processes.
Compare my reasoning
- Sedimentation lets suitable suspended solids settle.
- Filtration separates suitable remaining solid particles.
- Neither school-model description proves complete removal of all dissolved chemicals or microbes.
Settling plus filtration remove suitable solids, without establishing complete chemical or microbial purity.
Look for these in your work
- Both physical processes are distinguished.
- The conclusion stays within the supplied model.
Explain why carbon treatment and chlorination are both present in the required route.
Give me a hint
Tastes/odours and microbes are different targets.
Compare my reasoning
- Carbon removes tastes and odours by its treatment role.
- Chlorination kills microbes in the stated description.
- Improved taste/odour alone does not demonstrate that microbes have been killed.
Carbon targets tastes/odours; chlorination targets microbes, so their purposes are distinct.
Look for these in your work
- Each treatment has its required job.
- One favourable observation is not substituted for the other target.
A report proposes omitting chlorination from a supplied domestic treatment model because sedimentation, filtration and carbon made the water clear and odour-free. Evaluate the argument.
Give me a hint
Ask whether the observations establish the target of the omitted stage.
Compare my reasoning
- Clarity supports solid-removal observations, and odour improvement supports carbon's stated role.
- Those observations do not establish absence or destruction of harmful microbes.
- Therefore the argument does not justify removing the stage whose required purpose is microbial disinfection.
Clarity and no odour do not establish microbes killed; they cannot justify the proposed omission in this model.
Look for these in your work
- The existing stages' benefits are retained.
- The missing microbial evidence is identified.
Common mistakes
- Assigning chlorination only the job of removing large particles.
- Claiming carbon taste/odour removal proves all microbes killed.
- Assuming a classroom filter removes every dissolved salt.
- Presenting the syllabus flow as an unsupervised drinking-water recipe.
What can you explain now?
Which required treatment step kills microbes?
Compare with the explanation
Chlorination.
Its disinfection role differs from removing solids and tastes or odours.
After trying it yourself, choose your next review. This is your self-assessment.
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Make it stick
Draw the required treatment flow, label every stage's target and explain why a clear filtrate is not evidence of complete purification.
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.