Home / Hands-on activities / Emergency Water Filter Design Challenge

Engineering activity

Emergency Water Filter Design Challenge

Pretend you're a helper after a big storm and the tap water is muddy! Test 3 different materials to see which helps clean dirty water best. (Note: real emergency drinking water also needs boiling or disinfection — this activity is about engineering, not drinking.)

Hands OnAbout 20 minutesScreen-freeParent help expected

Materials and setup

How this changes by age

Pre-K (ages 3–4)

Pretend you're a helper after a big storm and the tap water is muddy! Test 3 different materials to see which helps clean dirty water best. (Note: real emergency drinking water also needs boiling or disinfection — this activity is about engineering, not drinking.)

Difficulty 1 of 3

Steps

  1. Pretend scenario: 'A storm knocked out the clean water. We need to engineer a helper!'
  2. Mix some dirt, small leaves, and water in a jar to make 'dirty water.'
  3. Get 3 cups. Put cotton balls in one, a coffee filter in another, and sand in the third.
  4. Pour a little dirty water through each cup into a clean cup below.
  5. Look at the water that came through each one. Which one is clearest? Which would you pick as the 'helper'?
  6. SAFETY: This water is just for LOOKING, never drinking — even clear water can have invisible germs.
  7. Tell a grown-up one thing that surprised you.

Learning objectives

  • Observe that some materials can remove dirt from water
  • Compare filtration results from different materials
  • Understand the basic concept of water filtration

Kindergarten (ages 5–6)

Build a water filter in a bottle using layers of sand, gravel, and cotton. Test it with dirty water and see how clean you can get it!

Difficulty 2 of 3

Steps

  1. Cut a plastic bottle in half. Turn the top half upside down and place it in the bottom half like a funnel.
  2. Add layers from bottom to top: cotton balls, fine sand, coarse sand, small gravel, large gravel.
  3. Make dirty water by mixing water with soil, food coloring, and small debris.
  4. Pour the dirty water through your filter. Collect the filtered water below.
  5. Is it cleaner? Pour the filtered water through again. Is it even cleaner the second time?
  6. Draw your filter showing each layer and what it catches.
  7. Tell a grown-up one thing that surprised you.

Learning objectives

  • Build a multi-layer filtration system with different-sized materials
  • Understand that each layer catches different-sized particles
  • Observe that multiple filtration passes improve water clarity

Early elementary (ages 6–8)

Practice the ENGINEERING DESIGN CYCLE: design a filter v1, test and measure it, then improve to v2 and measure the improvement. This activity is about how engineers iterate, not about water science (for the science side, see sci-053).

Difficulty 2 of 3

Steps

  1. Design FILTER v1: sketch your first filter on paper. Write down the layers you will use (e.g., cotton + sand), the material cost in pretend dollars (e.g., cotton = $1, sand = $1, gravel = $1, charcoal = $3), and why you chose it.
  2. Build v1 in a plastic bottle. Make a standard 'dirty water' (water + soil + a drop of food coloring) and pour the same amount through.
  3. MEASURE v1 with a data table. Columns: Design, Drip speed (seconds per 100 mL), Water clarity (1-5 where 5 = read through it easily), Material cost ($). Fill in the v1 row.
  4. REFLECT: what did v1 do well? What did it do badly? Pick ONE thing to improve in v2 (e.g., add a charcoal layer to fix color, or add more gravel on top to speed up drip).
  5. Design and build FILTER v2 with your one improvement. Run the exact same test and fill in the v2 row of your table.
  6. Compare v1 vs v2 row by row. Did your improvement actually help? Did anything get worse (e.g., slower drip, higher cost)? This is called a TRADE-OFF — real engineers face it every time.
  7. Optional v3: fix a new issue and measure again. Each version is one turn of the design cycle: design → build → test → measure → improve.
  8. In one sentence, tell a parent or sibling what surprised you today.

Learning objectives

  • Apply the engineering design cycle: design, build, test, measure, improve
  • Record quantitative results across versions in a structured data table
  • Recognize trade-offs between competing metrics (speed, clarity, cost)

Upper elementary (ages 8–10)

You're a humanitarian engineer designing a low-cost field filter for a disaster-response kit. Engineer THREE competing designs and optimize them as a multi-variable trade-off problem: clarity, color removal, AND flow rate. (For the municipal / scientific comparison, see sci-053.)

Difficulty 3 of 3

Steps

  1. Constraint brief: your filter must be buildable from supplies a family would plausibly have after a disaster (plastic bottle, cloth, sand, gravel, charcoal from burnt wood, coffee filter).
  2. Test each with water contaminated with soil particles, food coloring (simulating dissolved contaminants), and a drop of cooking oil (simulating floating contaminants).
  3. Measure three metrics: particle removal (0-5 clarity scale), color removal (compare to control cup), and flow rate (ml per minute).
  4. Build a decision matrix: weight each metric (e.g., 50% clarity, 30% color, 20% speed). Calculate a weighted score for each design.
  5. Iterate: pick the winner and improve it once. Does your modification raise the score?
  6. Write a design brief (not a scientific report): recommend ONE final design to a disaster-response charity, with a pros/cons list, a cost estimate, and a clear statement of what this filter does NOT do (kill germs, remove dissolved chemicals — boiling or disinfection still required).
  7. In one sentence, tell a parent or sibling what surprised you today.

Learning objectives

  • Apply real water treatment engineering principles to design a filtration system
  • Measure and optimize multiple performance metrics simultaneously
  • Analyze how different filter media target different types of contamination

Safety and evidence note

Read the full activity before beginning. An adult should supervise tools, heat, food, outdoor work, movement, and experiments as appropriate. Completion records that the activity was done; the child’s explanation, work sample, photo, or demonstration is stronger evidence of learning than a completion check alone.

Related engineering activities

Arch Engineering

Build an arch using blocks or cardboard pieces. Discover the magic of the keystone — the piece that holds everything together!

Balloon Rocket

Thread a string across the room, tape a balloon to a straw on the string, and watch it zoom when you let the air out!

Boat Engineering

Build a boat from aluminum foil that floats in a tub of water. See how many pennies it can hold before sinking!

Bridge Builder Challenge

Build a bridge using blocks, cardboard, or popsicle sticks that can hold a toy car or small stuffed animal.

Browse all 575 activities · Explore course syllabi