Lesson 6: To Filter or Not to Filter

Grade 5-8 (Science and Social studies)
Grade 9-12 (Science and Social studies)

Topic: Filtering polluted water

Time: 60 minutes

Space Requirement: Regular classroom

Methodology: Lab, cooperative learning

Materials: Price tags, 1 2L pop clear pop bottle per group, 1 500-mL pop bottle (with lid)per group, 1 cup of fine sand per group, 1 cup coarse sand per group, 1 cup fine gravel per group, 1 cup coarse gravel per group, 1 cup activated carbon (charcoal) per group, 1 cotton ball per group, 1 clear cup per group, 1 small piece (about 10 cm3 ) per group, 1 rubber band per group, monopoly money, TDS meter, pH meter. 

Pollutant Materials Required: dirt, food colouring, dish detergent, organic matter (such as coffee grounds or opened tea bags), oil, molasses, the pollution sample from the day before.

Before the lesson: prepare the following pollution solutions and pour each one into a labelled 500 mL pop bottle (label with group number only):
a. Group 1: water, dirt, food colouring, dish detergent, organic matter (such as coffee grounds or opened tea bags), and a little oil (1-2 teaspoons).
b. Group 2: water and molasses
c. Group 3: water, dirt, molasses, food colouring, oil (2-3 tablespoons), coffee grounds or opened tea bags
d. Group 4: water and food colouring
e. Group 5: water, dirt, mollases, food colouring, oil (2-3 tablespoons), coffee grounds or opened tea bags
f. Group 6: the pollution sample from the day before (no preparation required)

Objectives: Students will construct a water filter in order to understand the complexity of cleaning polluted waters. Students will also develop an understanding of the complex economics regarding water cleanup and the differences in available resources among different countries.


  1. Prepare the materials.
    a. Cut the bottoms off the 2L bottles so they are ready to be made into filters.
    b. If using cheesecloth, cut it into 10cm X 10cm pieces. Coffee filters can be substituted for cheese cloth.
    c. If the charcoal is in large pieces, break them down a little using a hammer. There should still be pieces but not dust.
    d. Label the filter items on the table with the price tags (see Resources).
    e. On the board draw the chart (see Resources). Each group must copy the chart on to a separate sheet of paper, fill it in, write the group members names on it and hand it in at the end of the lesson.
  2. Assemble the group packages. Each group receives a handout that includes a group description and instructions on how to make the water filter or permission to build the filter they designed.
  3. Explain the activity to the whole class before they get into the groups from the previous lesson. (3 min)
    a. The person responsible for materials comes to pick up an instruction package and water sample and go back to the group.
    b. The person responsible for reading the procedure will read the activity to the group.
  4. Groups reform, pick up their instruction package and water sample and begin the activity. (2 min)
  5. Allow the students time to process the cost of building the filters and prompt the banker to collect the needed money to by supplies and then call the class to attention. (5 min)
  6. Explain that clean water comes at a cost and then give each group Monopoly money according to the list below. (5 min)
    a. Group 1: $50
    b. Group 2: $250
    c. Group 3: $250
    d. Group 4: $60
    e. Group 5: $50
    f. Group 6: $100
  7. Groups build the filters and filter their polluted water samples. Students will measure the TDS and pH of their unfiltered and filtered samples. (20 minutes)
  8. Each group must present their water samples and explain how they built their water filters (especially if they didn’t have enough money to do so) and explain how they think the filter performed. (20 min)
  9. Students hand in the page with the chart. Assign the writing assignment as homework by writing the topic on the board. (5 min)
    a. The water filter activity showed that water filtration practices are not all equal. Countries across the world have different amounts of money available to clean water and they may or may not have access to fairly clean water. Write a story about a person who has been affected by water pollution and what they would like governments to do to fix the polluted water.
  10. Remind the students to fill in their water bottle charts.

Evaluation: Each student will complete a writing assignment about his or her experience in this activity. The details for the assignment can be found below in the Resources section.

For the Teacher: This lesson is adapted from three sources: Engineers without Borders, Carmen Hood from the SEER water Project and Tracy Webb a teacher from Nova Scotia and a member of the Board of Directors for the Safe Drinking Water Foundation.

The goal of this lesson is for students to become aware of the challenges surrounding water pollution and filtering. They should also gain an understanding of the difficulties in filtering water when money is scarce and resources are expensive. It is advisable to have an EA or another teacher in the classroom during this activity especially for grade 5-7 to assist with filter construction and the filtering process.

If this activity is being performed after a weekend then the bottles of polluted water should be stored in a fridge over the weekend to prevent molding.

The students will very likely be concerned about paying money for the materials for the filters. Play this up a bit so that the students can make the connection between clean water and the cost of making water clean.

There are discussion questions available for the teacher to stimulate discussion after the activity (see Resources).

Resources: The resources for this activity are available through the following links:

Extension Activity: The Safe Drinking Water Foundation has other educational programs that can be taught with this set of lessons. Operation Water Drop looks at what chemical contaminants there are in water and is designed for a science class. Operation Water Flow looks at how water is used and where it comes from and is designed for a Social studies and Math collaboration. Operation Water Spirit presents a First Nations perspective of water and water issues and is designed for a Native Studies class. Operation Water Health looks at common health issues surrounding drinking water in Canada and around the world and is designed for a Health, Science and Social Studies collaboration. To access more information on these and other educational activities visit the Safe Drinking Water Foundation website at www.safewater.org.