How to Build Filters Out of Water Bottles

Written by vivian gomez
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How to Build Filters Out of Water Bottles
Make a water filter with an empty plastic water bottle. (pouring water from a bottle image by ElsSh from

You can make your own water filter by using empty plastic water bottles. Making a water bottle filter makes for an excellent science project. Students can learn about water pollution and what steps are necessary to clean polluted water. Knowing how to make a water bottle water filter also comes in handy for outdoorsy-types who can find only dirty water. You can make a cheap and effective water filter with an empty plastic water bottle, some gravel and sand and a few basic household materials.

Skill level:

Things you need

  • 1 plastic water bottle
  • Scissors
  • Knife
  • 1 plastic straw
  • Cotton balls
  • Fine-grain sand
  • Large-grain sand
  • Fine-grain gravel
  • Large-grain gravel
  • Dirty water (to test the filter)

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  1. 1

    Cut the bottom off a water bottle with scissors and discard it. You will work with the top half of the water bottle. Puncture a hole in the bottle's lid carefully with a knife to accommodate a plastic straw. Insert a plastic straw halfway through the hole in the lid.

  2. 2

    Place cotton balls at the neck of the half-bottle, surrounding the straw. The cotton is the lining of your filtration devise and will be the final buffer before the filtered water comes out through the straw and into a glass or mug.

  3. 3

    Place a layer of fine-grain sand over the cotton balls. Place a layer of large-grain sand on top of the fine-grain sand, then layer of fine-grain gravel, and finally a layer of large-grain gravel on top of that. Keep alternating the layers in this order until you reach the top of the bottle.

  4. 4

    Place a coffee filter on top of the cotton, sand and gravel layers.

  5. 5

    Test your filtration devise. Place a clean mug or glass under the straw of the filter you made. Get a glass of water and throw in some torn bits of paper, food colouring and cooking oil. Pour dirty water into the water bottle water filter through the coffee filter. The gravel and sand layers help trap impurities and the cotton catches sediment. The filtered water passes through the straw and into your glass or mug and is free of the pollutants you added.

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