Design Challenge: Stinky City Needs Clean Water!

Prompts and questions to ask the students

  • Where have you seen dirty water? What was the dirt in it?
  • Can you use dirty water? Why not?
  • What needs to be done to clean dirty water? How many steps can you think of?
    • Big debris
    • Small debris
    • Color and Taste and Smell
    • Germs and bacteria (purity)
    • More?
  • Can you think of ways that each type of impurity can be removed to make the water safe?
  • Can we drink sea water? Can we drink steam/river water? Can we eat freshly fallen snow? Why?
  • How does water flow? Bottom to top? Top to bottom?
  • Natural water movement in waterfalls, streams, lakes, ocean. How can we use that?

Before starting on your design, watch this video about the science behind water filtration. Listen for scientific ideas for your filter design

Stinky City has a problem. Their lake water is polluted and is stinking up the town. They hire you as their Civil engineer to help them. You get to decide how to help Stinky City. The lake sits just above Stinky City, and there is a river just below Stinky City. The residents of Stinky City have learned that it’s a problem if they do not clean their water before releasing it into the natural body of water, so they need your help to treat the water from their lake before it goes to the river. You know that an aqueduct, composed of a connection of pipes, uses gravity and the slope of the land to transport water from a higher elevation to a lower elevation. In order to get approval from the city, you must show how your design meets the performance criteria set by the city. Use the materials provided (plus anything from home you’d like to add) to create a system that gets the water as clean as possible as it moves through the pipes that carry the water from the lake, down to the river.

Performance Criteria:
1. Avoid as much water loss as possible (Efficiency)
2. Get your water as clear and free of contamination as possible (Effectiveness).

  • White Bucket (to catch the filtered water at the end)
  • Scissors
  • PVC pipes
  • Empty water and soda bottle
  • cardboard cylinders
  • Sponge
  • Variety of fabrics
  • Cotton Balls
  • Activated Carbon/Charcoal
  • Masking tape
  • Coffee filters
  • Any other items around the house that you want to include

Final test material

  • Graduated cylinder
  • 1 bottle of water
  • Water Test Strips
  • Baggie of Contaminant

Step 1: Design
Sketch a water transport pipeline with filters placed strategically within the system so that the Stinky City residents’ wastewater can become as clean as possible.

Step 2: Build a Prototype
Use the materials you’re given (and/or items from home and classroom) to build your water transport and filtration system. Be sure to record a list of the items you used and show their location on your drawing from Step 1.

Step 3: Test and Improve
Test your design by running tap water through the system. How can you make sure the water doesn’t go down too fast? How can you make sure there’s no leakage through your pipes? How can you make sure you don’t overwhelm your water transport system with too much water? Change your design as many times as you like to get it as effective as possible.

Step 4: Final Test 
Open the provided bottle of water. Pour about 5 caps full of the bottled water into a cup or glass to use for comparison (set it aside). In a container larger than the bottle of water, mix the sediment and the rest of the bottled water. Shake it well and let it sit for an hour before your test. This is your model for the dirty lake water that you will use for your final filter demonstration. Before the test, shake the dirty water again and then pour 5 caps full of the dirty water into a cup or glass to use for comparison (set it aside). Be sure to label your comparison samples so you can tell them apart at the end of the experiment.

  1. Use the graduated cylinder to measure 10 ounces (oz) of dirty water that you will put into your filtration system (record the amount in the space below)
  2. Pour the dirty water from the graduated cylinder into your filtration system. Catch the filtered water in the clean white bucket at the bottom.
  3. Carefully pour the filtered water back into the graduated cylinder to measure how much clean water you end up with (record the amount in the space below)
  4. Test your design using Stinky City’s lake water. Use a Drinking Water Test Strip to test Stinky City’s Lake water after going through your water transport system. What is the difference? How much water is leftover?

Final Outcomes:

(a) Started with ___10___ oz of dirty water.

(b) Ended with____________ oz of filtered water.

Total water loss = (a) – (b) = ____________ oz


  1. Visual Test: Show the difference between the clean water, the filtered water, and the dirty water with a photo of all three side-by-side. (visual test)
  2. Contaminant Test: Use the water testing kit to measure the contaminants left in the filtered water.

In the Water Testing kit (provided), you will find the following:

  • Clear plastic vial with white cap
  • Alkalinity/pH/hardness test strip (in foil packet)
  • Iron test strip (in foil packet)
  • Iron reagent tablet (in foil packet)
  • Chlorine/copper/nitrate/nitrite test strip (in foil packet)
  • Instructions and color chart

Water Testing Instructions (video instructions are on the website)

  • You will run 3 different tests with your remaining filtered water.
  • Conduct the tests by the sink so you can rinse out the clear vial in between
    each test.
  • Read the instructions included in your water testing kit. Note that you should
    rinse the vial and fill with a new batch of dirty water for each test. There are 3
    tests total.
  • Follow the instructions included in your water testing kit.
  • Record your results below.

Alkalinity: _______________ ppm
Hardness: _______________ ppm
pH: _______________ –
Iron: _______________ ppm
Total Chlorine: _______________ ppm
Copper: _______________ ppm
Nitrate Nitrogen: _______________ ppm
Nitrite Nitrogen: _______________ ppm

  • What worked? Why? What challenges did you face?
  • How can these concepts be applied somewhere else?
  • How is your design unique?
  • How and when do you see these concepts in day-to-day life?
  • Where can you apply these concepts to improve something you are doing?
  • What materials did you use to filter and transport? Why? What else COULD you have used
  • Note: Take photos and explanations from students. Ask them to make posters/ diagrams etc to explain what they learnt

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