Water Purification

6, 7, 8

The learners experiment with a natural water filtration process. They review the water cycle and come to an understanding about the need to sustain the quality of the world's water for the common good. 

PrintOne 45-Minute Session

The learners will:

  • define environmental stewardship as the careful and responsible management of our environment.
  • identify the stages of the water treatment process.
  • review the water cycle.
  • determine the need to sustain the quality of the world's water.
  • Large strainer
  • Coffee filter
  • 1/2 inch layer of sand
  • Inch of top soil
  • A cup to hold dirty water
  • environmental stewardship: the careful and responsible management of our environment.
  • sustainability: a method of using resources so they are not damaged permanently (preserved for future generations)
  • What process do you think the city should use to purify/clean the water you drink?
  • How can we be responsible with water?
  • Is safe drinking water a a want or a need? Why?


  1. Anticipatory Set

    Ask for a few student volunteers to read their reflection paragraph responding to a quotation of their choice.

  2. Set up the following as a demonstration or provide enough supplies for youth to do it as an experiment. Line a medium-size strainer with a coffee filter. Add a 1/2 inch layer of sand and an inch of top soil. Put the strainer over a clear jar. Tell the students that this demonstration represents the natural water treatment process. This is how nature treats storm water flowing over a natural area with healthy drainage. Stir 2 tablespoons of dirt into a cup of water, then pour the dirty water through the sand and soil in the filter. Ask the students to observe the water in the bottom of the container and the condition of the sand and soil.

  3. How does the water look different after it goes through the ground filter?

  4. What other kinds of dirt or waste do you think this filter system will clean up? Try some of their proposals, if possible.

  5. Ask: What kinds of pollution do you think might not be filtered out by this natural process? Would you drink the water if it was polluted with chemicals, detergents and fertilizers? (The sand and soil might not be able to clean the water.)

  6. Remind the students that the Earth is a closed system—no water is ever added to the system over time, and we share the water with everyone in the world. For that reason, we need to be responsible with the water we use. Hold up the glass of filtered water. Tell the students that the H2O molecules of water in this glass may have fallen on the heads of dinosaurs, washed the hands of Civil War soldiers, satisfied the thirst of Olympic athletes or flowed down the Amazon River along with the crocodiles. Ask: How can that be? Allow students to conjecture, then remind them of the water cycle: precipitation, infiltration, evaporation, condensation, precipitation. Show the diagram at https://water.usgs.gov/edu/index.htmlwatercyclehi.html if internet access is available.

  7. Summarize for the students that polluted water affects us all now and in the future because water is a common resource we share with all people and animals. What we do locally ends up in the global water system. Water is never created; it is recycled and shared repeatedly. Water is a common resource and its quality must be sustained for the common good.