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Classroom activity Kindergarten Engineering & Design

Duckville Pond Filter Test: Comparing Two Simple Water Filters

A kindergarten engineering activity where small groups build and test two simple water filters, then compare which one leaves cleaner water for toy pond ducks.

Objectives

  1. Students will build two simple filters from different everyday materials.
  2. Students will test both filters on the same cloudy water and observe what each one catches.
  3. Students will compare the two test results and identify which filter left clearer water.

Vocabulary

Filtration
Filtration is the step where water passes through layers of sand, gravel, or other materials that trap the small particles still left in it. It works like a very fine strainer.

Teacher overview

The toy ducks at pretend Duckville pond need clean water after a rainstorm stirred up mud, and this activity puts students in charge of solving that problem with two simple filter designs. The setup teaches the concept directly: each cup with a liner is a small model of a real water filter, and holding the two catch cups up to the light lets students see, with their own eyes, that different materials remove different amounts of dirt. A common misconception this activity addresses is that any filter removes all the dirt equally well; testing two different liners side by side shows students that a filter's material changes how well it works.

Run this in small groups of 3 to 4 so every student gets a turn pouring, holding a cup to the light, or recording the group's result. The pond water is for looking only, so remind students not to taste or drink it, even after it has gone through a filter.

Activity Directions

  1. Explain the problem: Duckville's pond got muddy after a pretend rainstorm (a spoonful of cocoa powder or fine dirt stirred into a shared cup of water), and the toy ducks need clean water again.
  2. Show the class two filter tools, built ahead of time or together: Filter A is a clear cup with a paper towel folded into a cone and tucked inside as a liner; Filter B is a clear cup with three or four cotton balls packed loosely inside as a liner. Before class, an adult pokes several small holes in the bottom of each filter cup so the water can drain through.
  3. Put students into groups of 3 to 4. Give each group one Filter A, one Filter B, two empty clear catch cups, and a shared cup of muddy "pond" water.
  4. Have one student in each group pour half of the muddy water slowly through Filter A into catch cup A, while a second student pours the other half through Filter B into catch cup B.
  5. Hold catch cup A and catch cup B up to a window or a lamp and compare which one looks clearer. Then look inside each filter's liner and count how many big brown clumps of dirt got caught there.
  6. On the two-column recording page, each group draws a happy duck face under whichever catch cup looks clear enough for the toy ducks, and a sad duck face under whichever one still looks too muddy.
  7. Groups that finish early may test a third idea, a filter lined with small clean pebbles, using a fresh cup of muddy water, if time and materials allow.
  8. End the activity after every group has tested both Filter A and Filter B and drawn a result on their recording page, roughly 20 minutes into the session; gather the class for the debrief.

From Water for Schools (waterforschools.org). This material is in the public domain (CC0) and may be copied, edited, and shared freely.

Answer Key
  1. Answer: In most groups' tests, Filter A (the paper towel liner) catches more dirt clumps and leaves clearer water, because paper towel material has smaller gaps between its fibers than a loosely packed cotton ball, so more dirt gets trapped before the water passes through.
  2. Debrief question: "Which filter left clearer water for the ducks, and why do you think it worked better?" Answer: Filter A usually worked better because its material has smaller openings, catching more dirt clumps; accept any answer that correctly identifies the filter the group actually observed as clearer, with a reason about the liner material.
  3. Debrief question: "What would happen to the ducks if the pond water was never filtered after the rainstorm?" Answer: The ducks would have to swim in cloudy, dirty water, which is why cleaning the water first, the way a real water treatment plant does, matters for the animals and people who use that water.

Differentiation

Support (below grade level)

Pre-build both filters before class so students only need to pour, observe, and compare, rather than assembling the liners themselves. Provide a simple two-picture choice card (clear cup / cloudy cup) for the recording page instead of a drawn duck face.

Extension (above grade level)

Ask groups to design and test a third filter using a material of their choice (a coffee filter, a small square of cloth) and explain, using the word "material," why they predict it will work better or worse than Filter A and Filter B. Have them count and record the exact number of clumps each of their three filters caught.

ELL supports

Pre-teach filter, clear, cloudy, and material with a simple before-and-after picture of muddy water becoming clear. Allow students to show their comparison answer by pointing to the clearer catch cup rather than saying a full sentence, and pair the word "filtration" with the physical action of pouring through a liner.

Extensions

Visit or video-call a local water treatment plant, if one offers classroom outreach, and ask an operator to show a real filter and explain what it catches in one sentence students can understand. Extend the activity at home by having students test a coffee filter with a parent using a cup of water with a pinch of dirt, which is not for drinking, then report back what they saw the next day.