Water Filtration Experiment

This experiment will help you to understand why plants are so important! You will learn about how water filters through the soil and how plants affect that filtration. Through this experiment, you will test 3 different variables to see which produces the cleanest filtered water.

The 3 water filtration environments you will test are:  

  • Regular potting soil with nothing else in it
  • Regular potting soil with woodchips on the surface
  • Regular potting soil with flowers planted in it

Before you get started with this project, do you have a prediction on which soil environment will produce the cleanest water?

 Photo by LifeIsaGarden.co.za

Photo by LifeIsaGarden.co.za

What You'll Need

  • 6 bottles, all the same size (you can use 2L pop bottles, 4L milk jugs, or even 500mL plastic water bottles!)
  • Potting soil (you can buy some at your local greenhouse for a low cost if you don't have any)
  • A piece of plywood or cardboard that will fit 3 of your bottles on it
  • Hot glue gun
  • Permanent marker
  • Some potted plants that will fit inside of one of your bottles (petunias are perfect, and are inexpensive to purchase at your local green house)
  • Woodchips or mulch (which can be collected or also purchased at a local greenhouse)
  • Hole punch
  • String
  • Scissors
  • Water

What to Do

  1. Using a permanent marker, draw an outline for a large opening on the side of 3 of your bottles. (Use the photo above for reference about how large to make the holes)
  2. Get an adult to help you cut open the bottles along the outlines that you drew.
  3. With the help of an adult, use a hot glue gun to attach the 3 bottles to a piece of cardboard or plywood, with the openings of the bottles facing up.
  4. Cut the other 3 bottles in half horizontally so that you only have the bottom half of the bottle to use as a collection cup for the filtered water at the end.
  5. Using a hole punch, make two holes (one across from the other) in each of the collection bottles to be able to attach string to hang them.
  6. Cut out 3 pieces of string to attach to each of the bottles you just hole punched. Tie the string on like a handle, so that you can hang these bottles from the necks of the ones attached to the plywood. 
  7. Once you have the collection bottles hanging in place on the necks of the 3 filtration bottles, add soil to each filtration bottle through the large opening you cut out in the second step.
  8. Now for the variables! You are trying to test to see which soil environment will produce the cleanest water, so do the following with each of your filtration bottles:
    • Leave one of the three bottles with just soil in it
    • Add woodchips to the surface of one of the bottles
    • Plant some flowers or other type of plant (an already growing plant, not just seeds) in the last bottle
  9. If the caps aren't already removed from your filtration bottles, remove them now.
  10. Pour an equal amount of water into each of the filtration bottles until you start seeing the water flow out of the cap and into the collection bottles.
  11. Compare the water that has filtered through each type of soil environment and collected in the hanging collection cups. Which water is the cleanest? Was your prediction correct?

Ask Yourself

  • What do you see happening as the water filters through each bottle? Why do you think this is happening?
  • Imagine you have a body of water that will be used for bottled drinking water. Based on the results of your experiment, what types of soil or vegetation would you want to have around that water source? Why?
  • Why are plants important to keep ecosystems healthy?