Water purification

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Make a simple water filter using plastic bottle with a cotton, sand & gravel filter




2-liter soda bottle cut in half (by an adult)
napkins or paper towels
gravel, sand and cotton balls for your filter
dirty water, you can make it by adding cooking oil, food coloring, pieces of paper, and tiny pieces of Styrofoam to water


Put the top half of the soda bottle upside-down (like a funnel) inside the bottom half. The top half will be where you build your filter; the bottom half will hold the filtered water.
Layer the filter materials inside the top half of the bottle. Think about what each material might remove from the dirty water and in what order you should layer the materials. For an added challenge, use only two of materials to build your filter.
Pour the dirty water through the filter. What does the filtered water look like?
Take the filter apart and look at the different layers. Can you tell what each material removed from the water?
Wipe the bottle clean and try again. Try putting materials in different layers or using different amounts of materials.

Now it's time to experiment. Think of a question you want answered. Like, are there better materials for cleaning water? Be sure to predict what you think is going to happen. Then, test it out using different materials and send your reports in to our special feedback area. Every week, we'll publish a whole bunch.

[Edit: 14/3/17/David Hole: there is no longer a 'water' part of the scouts survival; if you are doing this with real dirty water (puddles/pond etc.) consider health risks - make sure they wash hands after, and have waterproof plasters over any cuts. Adding oil makes it feel disgusting! For Scouts, we left them to get on with it, with no hints. Materials that worked well: decorators paper face masks, cleaning sponges, sand (must be clean e.g. play sand). Cutting holes in water bottles is difficult without an electric drill! Debrief that filtering water should not be considered sufficient to make it safe to drink - needs boiling as well]


  • Global Challenge water
  • survival skills water
  • Water Purification

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  • Global Issues - Water filter
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  • Survival Skills - Water