Nature's water filter

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Biology in Middle Schools home | |Elementary School sister project
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Biology In Middle Schools is a Saint Michael's College student project. Link under 'toolbox' for a printer-friendly version. Click on handouts to print full resolution versions. Please see Wikieducator's disclaimer, our safety statement, and the Creative Commons licensing in English and in legalese.

Primary biological content area covered

  • Learning how water is naturally filtered through layers of soil, gravel and sand
  • Formation of a clear hypothesis
  • Experimentally testing a hypothesis
  • Using beakers to measure out a specific amount of water
  • Neatly writing observations in a notebook during the experiment


  • Materials required for the teacher's use
    • Scissors
  • Materials required for class
    • Potting soil
    • Sand (various grain sizes)
    • Gravel
    • Kitty litter
    • Pebbles
    • Clay (modeling clay)
    • Moss
    • Cheese cloth
    • Marbles
    • Charcoal (Carbon activated charcoal, found in aquarium supply stores)
  • Materials that each individual student/pair will need
    • 2, two-liter soda bottles (clear and plastic bottles)
    • Beaker
    • A cup of pond/murky water
    • Stopwatch
    • Handout
    • Rubber band


Description of activity

Prior to class the teacher will have prepared the materials. Half of the two-liter bottles will have had the "necks" cut off so that another bottle's neck may fit inside. The other half will have the bottoms cut off. All filter materials that the teacher has access to will be readily available for the students.

Students will observe the building materials available for them carefully, working either in pairs of two or alone. Next, they will write a clear hypothesis about which materials they will use to build their filter and the order in which they will layer them. It will be important for students to clearly define the thought process behind their choices and reason their hypothesis.

Depending on time availability, the actual experiment may occur right after construction of the filter, or during the next class period. The next part of the experiment is to have the students measure out a specific amount of pond/muddy water (50 mL or 100 mL) and pour it in the top of their filter. Students will time the percolation process using a stop watch and make observations in their notebooks.

Construction Details

To build the filter, first students will cover the neck of the inverted bottle with a cheese cloth and secure it with a rubber band. The cheese cloth is essential because it not only is a great filter it also allows water to escape while keeping all of the filter materials in the bottle. Next they will layer materials in what ever order they choose in the inverted two liter bottle with the bottom cut off. Once all materials have been added to the inverted bottle, the students will place the "filter" on top of the other bottle, being sure to hold it still. Duct tape® may be used to help steady the bottles and prevent leakage.

Lesson plan

This lesson should be built into a unit where students learn about the water cycle, groundwater, geology, and/or natural resources.

This lesson may work best in two parts depending on scheduling of your school. If on a block schedule, the whole lesson/experiment may be run in one class period.

-Handouts are given to students (3 minutes)
-Teacher introduces themes and the task assigned (5-10 minutes)
-Safety reminders, helpful hints (do not overfill, no floods, keep area clean) (3 minutes)
-Students gather into pairs and discuss the task and materials (10 minutes)
-Hypothesis and methods are recorded in notebooks/handout (5 minutes)
-Students build their water filter (20 minutes)
-Students add the water and record observations (15 minutes)

-Clean up: dumpster for all wetted soils and other materials, box for 2 liter bottles, wash hands and tables (15 minutes)
-Discussion of observations, shortcomings, errors, what worked and what did not, what to do next time (15 minutes)

Potential pitfalls

If students use too many dense materials in their filter or pack the materials tightly percolation can take a very long time.

The children may be exposed to bacteria and algae from the pond water they collect.


We estimate that each water filter can be made fairly inexpensively. Most of the necessary materials (clay, charcoal, sand) come in bulk and one bag of each will be enough for the entire class to use.

For students to estimate the effectiveness of their filter, it would be beneficial to set up a gradient to show different dilutions of the pond water. This way students can estimate the percentage of sediment removed from the pond water by their filter.

Add on

To further the educational adventure, consider using sites developed by other Saint Michael's classes such as: Your_Body:_A_Bacteria_Incubator! and Ew!_Gross!_Germs!

These two experiments will allow students to test their filters by growing different microorganisms from their pond water and from the filtered pond water.

Math connections

  • Rate -- have students measure how much water they add and how long it takes for the water to travel through the filter (liters/minute)
  • Ratios/fractions -- how much of the water added was collected in the end?
  • One way to present the data for the entire class would be to make a graph of the clarity versus time of percolation.

Literature connections

  • Making Water Clean by Rebecca Olien
    • Olien, Rebecca. 2005. Making Water Clean. Capstone Press.
  • Water; Our Precious Resource by Roy A. Gallant
    • Gallant, R. 2003. Water; Our Precious Resource. Marshall Cavendish.

Connections to educational standards

Geographic Knowledge: 6.7 Students describe such spatial patterns as population distributions, land use patterns, climate, transportation networks in Vermont, the United States, and the world.

Scientific Method: 7.1 Students use scientific methods to describe, investigate, explain phenomenon, and raise questions in order to: generate alternative explanations; design inquiry that allows these explanations to be tested; deduce the expected results; gather and analyze data to compare the actual results to the expected outcomes; and make and communicate conclusions, generating new questions raised by observations and readings.

Scientific Investigation: 7.2 Students design and conduct a controlled experiment

Systems Analysis: 7.11 Students demonstrate understanding that systems are connected to other systems, and that one system affects how others work; Demonstrate understanding that systems are effectively designed when specifications and constraints are understood.

Organisms, Evolution and Interdependence: 7.13 Students understand the characteristics of organisms, and recognize the interdependence of all systems that support life; Describe, model, and explain the principles of the interdependence of all systems that support life (e.g., food chains, webs, life cycles, energy levels, populations, oxygen-carbon dioxide cycles), and apply them to local, regional, and global systems.

Theories, Systems, and Forces: 7.15 Students demonstrate understanding of the earth and its environment, the solar system, and the universe in terms of the systems that characterize them, the forces that affect and shape them over time, and the theories that currently explain their evolution This is evident when: a. Identify and record evidence of change over time, e. Analyze and explain natural resource management.

Next steps

  • Possible visit/tour of the local water treatment facility.
  • How difficult is it to remove certain pollutants from our water?
  • What is left in our water in terms of chemicals or metals?
  • What other information or materials could be used to make a better filter?
  • Pollution's effect on ecosystems and human health.
  • How much pure water do we dirty in one day?
  • Ask students to think about how much water they use at home or in school and discuss water conservation and different ways to conserve water.
  • Construct another water filter, but this time place cheese cloth between each of the filter materials you use. Does the cheesecloth enhance the purity of the filtered water?


Edit this section after you have tried the activity with grade school students. What worked well? What was unexpected? What previous knowledge did the students bring to the activity and how did that compliment your lesson? Are there any must do components that did or would particularly enhance the learning experience? Other helpful thoughts.

Citations and Links


  • This website has information for students and teachers on various topics concerning water such as: groundwater, hydrology and watershed.

| USGS Website

  • This site teaches kids about water, why it’s important and how they can help protect this natural resource. It also has various learning activities for students such as activity books and an interactive water cycle. | Environmental Kids Club Web Site
  • This website has various activities such as word scrambles, a word matching game and a fun facts game for students in grades 4-8. These activities were designed to teach students about groundwater, drinking water, and the water cycle. This website also offers different class room activities for teachers to help students understand the role plants play in water filtration, non-point source pollution, and the water cycle.| Drinking and Groundwater Activities for Students and Teachers


Basic Ground Water Hydrology [Internet] [cited 2009 Jan. 21] GWAC 7 p. Available from

Campbell, N., Reece, J.2002. Biology, sixth ed. Pearson Education, Inc., CA pp. 1210.

Drinking Water and Ground Water Kid’s Stuff. [Internet] [cited 2009 Feb. 23] USEPA. Available from:

Ecosystem Services-Water Purification [Internet] 2002 June 30 [cited 2009 Feb. 23] Science Net Links. Available from:

Environmental Kids Club.[ Internet] [cited 2009 Feb. 23] USEPA. Available from:

Give Students a Taste of the Water Filtration Process. 2005. 44:7 pp 7-8.

Gordon, J. 2008. How Do Our Actions Affect Ground Water Quality?. Science Scope.31:26.

Green, T. 1996. Watershed Science. The Science Teacher. 63: 35-36.

Rushton, E., Ryan, E., Swift, C. 2001. Water Filtration Grades 3-5. Tufts University, Medford M.A. pp. 1-6.

Solomon, G. 1983. Wet Worlds: Explore the World of Water. Marine and Freshwater Activities for the Elementary Classroom. Staten Island Continuum of Education. pp.4-76.

Vermont's framework of standards and learning opportunities[Internet]. Vermont Department of Education: Equal opportunities for an education of excellence; 2000 [cited 2009 March 1]. 73 p. Available from:

Water Filter Experiment [Internet] [cited 2009 Jan. 21] Aqua Ducks Water World 1 p. Available from

Water Science for Schools [Internet] 2008 Nov. 7 [cited 2009 Feb. 23] USGC Available from: