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In this lesson, students will compare polluted and filtered water to observe how filtering can remove some kinds of pollutants. Students will also be asked to consider how people affect ecosystems and use the scientific method to conduct an experiment on polluted water.

Grade Level

Elementary and Middle School


By the end of this lesson, students should be able to

  • Use the filtration technique to separate a mixture.
  • Compare polluted and filtered water.
  • Draw appropriate scientific conclusions given data from a scientific experiment.
  • Describe how people can have an effect on the ecosystem.

Chemistry Topics

This lesson supports students’ understanding of

  • Separating mixtures
  • Physical Properties
  • Chemical Properties
  • Observations


Teacher Preparation: 15 minutes

Lesson: 20-40 minutes


Per group:

  • 3 cups with lids
  • 3 cups without lids
  • 1 wax pencil
  • 1.5 cups of water
  • ½ measuring cup
  • 3 coffee filters
  • 3 rubber bands
  • Pollutants: 10 drops of food coloring, ¼ cup torn paper, 10 drops of vegetable oil, ¼ cup of cut strips of old towel, 10 drops of green dishwashing detergent, and ¼ cup of small pieces of bread.


  • Always wear safety goggles when handling chemicals in the lab.
  • Students should wash their hands thoroughly before leaving the lab.
  • When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.
  • Do not consume lab solutions, even if they’re otherwise edible products.
  • Food in the lab should be considered a chemical not for consumption.

Teacher Notes

  • Introduce the lesson by discussing the places we swim and the waterways around us. For example: in Louisiana you could introduce Kistachie National Park, discuss the water we fish and swim in while on a vacation. Introduce Lake Pontchartrain, Mississippi River, and the nearby bayous for discussion.
  • Use the suggested websites below to read about and discuss water and air pollution. Some text books in science and social studies also have great, relevant material:
  • Monitor student understanding through the experiment.
  • Students will filter 3 cups of mixtures, containing different combinations of pollutants to see just what pollutants get extracted.
  • Depending on the age and ability level of students, teachers may want to prepare these cups in advance, or allow students to mix the contents themselves.
  • Label the first cup “Pollutant 1,” this container will have the ½ cup of water, 10 drops of food coloring and ¼ cup of torn paper.
    • Expect to have some of the coloring get soaked up into the filter and therefore the rest to pollute the water when filtered. The torn paper will also filter out leaving the water cloudy (slightly polluted). This can be filtered more than once to see how much pollution they can get out of it.
  • Label the second cup “Pollutant 2,” this will also have the ½ cup water, 10 drops of vegetable oil, ¼ cup of cut strips of old towel to be filtered.
  • Label the third cup “Pollutant 3,”this one will have ½ cup of water, 10 drops of green dishwashing detergent, and ¼ cup of small pieces of bread.
    • Expect the green dishwashing detergent to leave bubbles and difficult to filter along with the pieces of bread. The bread begins to break down and create the haze in the bubbles. Pollution.
  • Extension Idea: Students can try sand as a filter agent to clean pollution from water. Conduct the same activity on household pollutants such as shampoo or lotion. Vermillion has a wonderful power point that discusses pollution in our waterways and leads into recycle, reduce and reusing material.

For the Student


Our oceans, lakes, bayous, and rivers can look like they are safe and clean, when in fact they may not be. Some of the solids and liquids we dump into the water will mix with water and can become invisible. Some things we put into water will not mix and we can see the damage with our eyes. Some natural chemicals are poisonous like sulfur dioxide from the combustion of coal, and carbon monoxide from automobiles exhausts. Some types of bacteria consume the poisons, and are similar to fertilizers we use on plants. Some poisons that humans have made can help the environment, and some can pollute much of the air we breathe, get into the food we eat and the water we drink or play in.


In this activity we will be reviewing and using the scientific method. We will be working through the scientific method step by step, using polluted water that needs to be filtered. The purpose of the experiment will be to compare polluted and filtered water.




1: Water, food coloring, torn paper

2: Water, oil, torn towel

3: Water, detergent, bread


  1. Place a lid on each of the 3 pollutant containers. Make sure it is secured tightly, and shake each cup vigorously.
  2. Remove the lid and record your initial observations of the pollution mixture.
  3. Record your initial observations for each mixture in the data table below.
  4. Obtain 3 empty cups, 3 coffee filters and 3 rubber bands.
  5. Push a clean coffee filter into an empty cup and secure it with a rubber band to hold in place. Using the wax pencil, label this “cup 1” to be used to filter the contents of “Pollutant 1.”
  6. Repeat step 5 with the two additional empty cups, labeling each as “cup 2” and “cup 3.”
  7. Starting with “Pollutant 1” pour approximately half of its contents onto the filter in “cup 1.” When the water has drained through the paper, remove the filter paper and compare the filtered water with the polluted water. Record your observations below.
  8. Repeat step 7 for the other polluted cups.
  9. Draw a picture of the polluted water and the filtered water for each mixture below.



Initial Observations

Comparison of filtered water and polluted water

1: Water, food coloring, torn paper

2: Water, oil, torn towel

3: Water, detergent, bread


Sketch of Polluted Water

Sketch of Filtered Water

1: Water, food coloring, torn paper

2: Water, oil, torn towel

3: Water, detergent, bread


Look back at the hypothesis you made at the beginning of the experiment. Based on the data collected, was your hypothesis correct? Why or why not?

Post lab questions

  1. How were the mixtures you filtered alike?
  2. Which pollutants were filtered out of each container?
  3. How did the filtered detergent compare to the mixture that was filtered?