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Ditch the dirt


Ditch the Dirt

(Suitable for Secondary School aged children)

Over 1/3 of the world’s population do not have access to clean water. In countries such as Kenya and Sudan, children have to journey many miles a day to collect water that isn’t very clean. If they are lucky they will have a way of filtering it. Your task is to design a filter!

What you need: 2 litre plastic bottle, variety of plastic containers to store your water, dirty water (a mix of mud, stones, twigs, leaves etc.) Materials to make layers e.g. stones, course sand, fine sand, gravel, cotton wool, measuring jug, paper towels, cloth, e.g. j-cloth Elastic band


  1. Make a container for your water filter. You can make a simple one by cutting through a 2 litre water bottle approximately one third up from the bottom, then inverting the top into the bottom. Alternatively, you can design your own using the other plastic containers
  2. Look at the materials available to you and discuss/research what type of contaminants they would be able to remove. Contaminants can be divided into biological e.g. bacteria and viruses, chemical, e.g. cleaning liquids and physical e.g. dirt or broken glass.
  3. Start to build your filter by experimenting with different materials and combining layers of material in different ways. Consider: The order of the layers and the depth of the layers. Changing these variables could alter how clean the water is and the rate of filtration, both are important.
  4. Pour 250ml of dirty water into the top of your filter and see how much (hopefully cleaner!) water you can collect in 5 minutes. Your aim is to collect at least 100ml.
  5. Stand 100ml samples of both the original dirty water and your cleaner water next to each other on a sheet of white paper to compare. You can even have a competition to see whose water filter has worked best! Consider why this may be.

Author: Caitlin Brown, British Science Association

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