What it shows
Muddy monsoon water can be made clear in stages: heavy soil settles, the clearer water is poured off, and a home-made sand and cloth filter removes the fine particles. The water looks clean but is still not safe to drink, which the project explains.
The science
Soil in water is a suspension: the particles are not dissolved and will settle under gravity if the water is left still, heaviest first. Decanting pours off the clearer top layer without disturbing the sludge. A filter is a bed of pores; particles larger than the pores are trapped while water passes. Layers of pebbles, sand and cloth trap smaller and smaller particles, and charcoal takes up some colours and smells. Dissolved substances and germs pass straight through, so clear water is not the same as safe water.
Materials
Cost: free. Many items come from home or from waste; spare parts such as LEDs, motors and wire are in the store.
- A bottle of muddy water made from garden soil
- Three clear jars or glasses
- A plastic bottle cut in half as a funnel (adult cuts)
- Clean cotton cloth, coarse sand, small pebbles and a few spoons of charcoal pieces
- A spoon
- White paper to judge clarity
Safety
For this project: An adult must cut the bottle. Never drink the filtered water; filtering removes particles, not germs.
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.
Step 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.
Shake the muddy bottle and pour half into a jar; hold white paper behind it and note how cloudy it looks.
Leave the jar untouched for thirty minutes and watch the layers of soil settle at the bottom.
Slowly tip the jar to pour the top water into the second jar without stirring the mud; this is decanting.
Rinse the charcoal and sand under the tap until the water runs clear, then build the filter in the upside-down bottle top: cloth over the neck, then charcoal, then sand, then pebbles on top.
Pour the decanted water gently onto the pebbles and collect what drips out below in the third jar.
Compare the three stages, muddy, decanted and filtered, side by side against the white paper.
Pour the filtered water through the filter a second time, catching it in the rinsed first jar, and see whether it gets clearer still.
Write a label for the display explaining why the clear water must still be boiled before drinking.
What you should see
Water turns from brown to nearly clear across the three stages, with mud left in the first jar and a brown stain on the filter cloth; a second pass improves clarity a little.
Viva questions
A teacher or a judge will ask how it works. Try to answer each question before you open it, then compare.
01Why do you wait before pouring?
So heavy soil particles can settle to the bottom under gravity.
02What is decanting?
Pouring off the clear liquid while leaving the settled solid behind.
03Why put sand below the pebbles?
Pebbles catch large bits first, and the finer sand traps the small particles.
04Is the clear water safe to drink?
No, germs and dissolved substances pass through; it must still be boiled or treated.
Take it further
Add a pinch of alum (fitkari) to a jar of muddy water, stir, and compare how much faster the mud settles.
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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