make a small filtration system

Particulates (black dots) being caught within the filter media (brown spaces)

Clean water is one of the earth’s most valuable resources. This water filtration system doesn’t make muddy water clean enough to drink, but it does show you how filtration systems work and how you can get most of the dirt out of water.

To make a water filtration system you need:

  • a cup of dirty, muddy water
  • a clean clay pot on a saucer
  • a coffee filter
  • crushed charcoal
  • clean, well-rinsed sand
  • clean, washed gravel
  • a sieve


  1. Open a coffee filter into the clay pot.
  2. Fill the bottom of the filter with some charcoal.
  3. Add wet clean sand on top of the charcoal.
  4. Put clean gravel on top of the sand.
  5. Hold the sieve over the pot and pour your dirty water through the sieve and filter.

See how much cleaner the water is in the saucer!

What’s the problem?
The dirty water contains many different elements that make the water “dirty” including but not limited to plant matter, minerals, sand, gravel, fine dust and grit.

  • Ask – Some of there materials are easily removed, but some are very tiny. How can the biggest impurities be removed? What materials are commonly used for water filtration? How can filtration of finer particles be achieved?
  • Imagine – The filtration materials are pressed together but there are always small holes and channels through the material layers. The holes in the coffee filter are smaller than the holes in the sand, for example. Any dirty that gets through the sand layer, will have to pass through the finer layers. Each layer will trap smaller and smaller dirty. How will the particles be removed from the water?
  • Design, Build – The filtration materials are arranged so the biggest particles will be removed first as the water flows through the system. The system depends on gravity to carry the water through the system. By the time the water gets to the coffee filter, most of the dirt will have been trapped in the layers of the filtration system. This water will look pretty clean. How should the filtration system materials be arranged to remove the dirt particles?
  • Improve – The water may also contain bacteria and other microbes but these are too small to be trapped with this simple filtration system. Some finer filtration and disinfection would be required to make this water clean enough to drink.

Engineering ideas

  • filtration, granular, particle, particulate

Learn more…

  • Fun Science Activities for Kids – used with permission