How Is My Water Purified? (Grades 8-12)

Subject: Biology, Chemistry, Science

Topic: The different ways of filtering water are explored.

Time Frame: 60 minutes

Objectives: The students will see the techniques that are used to filter their drinking water. They will get an idea of which pollutants can contaminate our water. The students will see the importance of keeping our water clean.

Methodology: Demonstration/Experiment, Discussion

Materials:

  • A large filtering tube and a long necked glass funnel, or 2 long necked glass funnels will work just as well
  • A large glass fish tank or jar
  • A bag of charcoal pebbles, sand, and gravel (this is available at a retail fish or pet store)
  • Filter paper
  • Petri Dishes
  • Chlorine (this is available at any retail store that sells swimming pool supplies)
  • A strainer or screen
  • “Pollutants” such as motor oil, coffee grounds, food colouring, paper, leaves, clay, etc.
  • A boiled potato, sliced

Space Requirements: There are no special space requirements for this lesson.

Directions/Procedure:

  1. Hand out the Question Sheet to the students. They will be able to fill this in as the demonstration is happening in front of them.
     
  2. Ask the students to define “pollution”. The students can fill in number one on their Question Sheet as correct answers are given.
     
  3. Ask the students what they think pollutes our water. The students can fill in number two on their Question Sheet as correct answers are given. As the students are giving answers about water pollutants, start “polluting” the clean water in the tank with the “pollutants”. The students can watch their water being “polluted” right before their eyes.
     
  4. Explain to the students that polluted water is first screened, then sedimentation takes place, then it is filtered, and then chemically treated. They can then fill in number three on their sheets.
     
  5. Pour some of the polluted water through the strainer, into a new container. Ask the students to record what they saw (ie. that the large particles were removed) under number four on their sheets.
     
  6. Ask the students what the next step of the process is. They should respond with “sedimentation”. The screened water can now be poured into a beaker or test tube and allowed to settle. The students can fill in number five on their sheets, recording also what they see.
     
  7. Ask the students what the third step of the process is and they should answer “filtration”. Fill the funnel first with a layer of pebbles, then a layer of sand, followed by a layer of charcoal. The second funnel should be lined with filter paper and held underneath the funnel with the pebbles, sand, and charcoal. This will provide extra filtration. The students can record what they see in number six on their sheets.
     
  8. The original polluted water tank should be looking clearer by now. Put a slice of potato in each of three Petri dishes. The potato is used as a growth medium in this experiment. On one slice, place a drop of the polluted water from the tank. On the second slice, place a drop of the filtered water from the funnel, and on the third slice, place a drop of filtered water from the funnel, and a drop of filtered water mixed with chlorine. Cover the dishes and leave them for a few days. The students should record their predictions on their sheets.

Evaluation: This can be used as a demonstration or as a full lab, if the materials are available.

References:

www.safewater.org

www.biology.about.com

www.iit.edu

Water Pollution Question Sheet

Name: _______________________________

  1. Define pollution.


     
  2. List 5 ways that water is polluted.
    a.
    b.
    c.
    d.
    e.
  3. List 4 ways in which water is filtered.
    a.
    b.
    c.
    d.
  4. What part of the water purification process was represented by pouring the polluted water through the strainer?



     
  5. What happened when the filtered water from the strainer was allowed to settle in a test tube and what is this process called?



     
  6. What happened when the water from the test tube was filtered through the sand and gravel in the funnel and what is this process called?



     
  7. What do you think will happen in the three Petri dishes?
    a. Dish 1



    b. Dish 2



    c. Dish 3
     
  8. Record your observations after looking at the three Petri dishes.
    a.



    b.



    c.


     
  9. Did the filtered water show any difference in bacterial growth than the polluted water?




     
  10. Did the filtered water mixed with chlorine show differences in bacterial growth than the other two drops?