What it shows
Cloth, sand, charcoal, alum and boiling each do different jobs. A homemade clarity tube ranks how well each method clears water, and the project explains which methods also remove germs.
The science
Straining with cloth and sand removes large particles, charcoal adsorbs colour and smell, and alum clumps fine particles. None of these on their own can be relied on to remove germs, which are killed by boiling or proper disinfection. The clarity tube shows how much light passes through the water.
Materials
Cost: under Rs 50. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- Muddy water made from garden soil
- Cotton cloth, a funnel, clean sand, crushed charcoal and gravel
- A pinch of alum
- A clear tube with a black dot at the bottom
- A measuring cup
- A pan for boiling (adult)
Safety
For this project: An adult must boil the water and handle hot items. Do not drink any water from the test. Charcoal dust is messy, so wear a mask when crushing.
Never use mains electricity: power models with cells, batteries or a low-voltage adapter. Sharp and hot tools, flames and lab chemicals need an adult or your teacher beside you. Keep magnets, button cells and small parts away from young children, and wash your hands after making.
All the safety rulesStep by step
8 steps. Do them in order, and test each part before you go on to the next. Write what you notice in a notebook as you go.
Make five equal batches of muddy water and test one in the clarity tube as the starting reading.
Method A: pour batch 1 through a cotton cloth.
Method B: pour batch 2 through a funnel filled with gravel, sand and charcoal layers.
Method C: stir alum into batch 3 and let it settle for 30 minutes.
Method D: let batch 4 settle for an hour without anything.
Method E: an adult boils batch 5 for five minutes and then lets it cool.
Pour each treated sample into the clarity tube and note the depth at which the dot is just visible.
Rank the methods by clarity and add a column on whether the method removes germs.
What you should see
The table ranks the methods for clarity, and the germs column shows that only boiling kills germs even though it does not clear the mud.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
1Which method removes mud best?
Usually the sand and charcoal filter with alum.
2Which kills germs?
Boiling.
3What does charcoal do?
It adsorbs colour and smell.
4Why is a clear water not always safe?
Germs and dissolved chemicals cannot be seen.
Take it further
Combine the steps in the best order to design a four-stage household treatment.
Change one thing, measure what happens, and add a table or chart of your readings: that is what turns a model into your own investigation.
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