💧 Water Filtration System
Build a multi-layer water filter using recycled plastic bottles, gravel, sand, and charcoal. Learn how communities get clean water — zero cost, 100% hands-on.
Why build a water filter?
Access to clean water is a global challenge. In this project, you'll build a simple but effective water filter using only recycled materials — a plastic bottle, gravel, sand, charcoal, and cloth. The filter removes visible dirt, particles, and some bacteria, demonstrating how real water treatment plants work. This project connects to CBC Science Strand 4: Matter and its Interactions (filtration as a separation technique).
Materials needed (all free or recycled)
- 🥤 2 empty plastic bottles (1.5L or 2L) – one for filter body, one as reservoir
- 🪨 Small gravel or pebbles (about 1 cup) – wash thoroughly
- 🏖️ Coarse sand (about 1 cup) – river sand works best
- ⚫ Charcoal pieces (from burnt firewood, crushed into 1cm chunks) – about 1 cup
- 👕 Clean cotton cloth (old t-shirt or handkerchief)
- 💧 Dirty water sample (muddy water from a puddle or mix soil with water)
- ✂️ Scissors or knife (for cutting bottles – ask an adult)
- 📸 Phone/camera for evidence photos
💰 Total cost: 0 KES (all items are household waste or free from nature).
Step-by-step build guide
Follow these steps to build your filter. Take photos at each stage for your SBA portfolio.
Prepare the filter bottle
Take one plastic bottle and cut it in half. The top half (with the cap) will be your filter — turn it upside down like a funnel. The bottom half will catch the filtered water. Remove the cap and place a small piece of cloth over the bottle neck, then screw the cap back loosely (or just lay the cloth on top).
Layer 1: Charcoal (bottom)
Add a 2–3 cm layer of crushed charcoal pieces into the upside-down bottle top. Charcoal removes chemicals and bad smells. Tap gently to settle.
Layer 2: Sand (middle)
Add a 3–4 cm layer of coarse sand on top of the charcoal. Sand traps smaller particles that charcoal might miss. Spread evenly.
Layer 3: Gravel (top)
Add a 2–3 cm layer of small gravel or pebbles on top of the sand. Gravel prevents the sand from floating away when you pour water. This is the first layer that catches large debris.
Test the filter
Place the filter top over the empty bottom bottle. Slowly pour dirty water into the top layer (gravel). Watch as water drips through the layers and collects below. Collect samples of "before" and "after" water in clear cups to compare clarity.
Compare & record results
Place the "before" (unfiltered) and "after" (filtered) water samples side by side. Take a comparison photo. Record observations: color, smell, visible particles. Filtered water is NOT safe to drink — it’s a demonstration of physical filtration only.
📊 KNEC SBA Rubric – Water Filtration Project
Your teacher will assess using this rubric. Maximum score: 20 points.
| Criteria | Exceeds (5) | Meets (4) | Approaching (3) | Below (2-1) |
|---|---|---|---|---|
| Materials & construction | All layers correct order, stable filter, no leaks | One layer slightly off, minor leak | Two layers wrong order, slow filtration | Filter collapses or doesn't work |
| Scientific method | Hypothesis written, variables identified, controlled test | Hypothesis but missing variables | No hypothesis but test done | No test plan |
| Data & observation | Detailed written + photo evidence, clarity comparison table | Observations written, 2 photos | Brief notes, 1 photo | No data recorded |
| Conclusion & application | Conclusion explains how filter works + real-world water treatment link | Conclusion but missing application | Weak conclusion | No conclusion |
Project Gallery – add your own images
Use these slots to document your filter building process.
🚀 Extension challenge (bonus marks)
Test how different layer orders affect filtration speed and clarity. Build a second filter with layers in reverse order (gravel at bottom, charcoal at top). Compare the two results. Write a paragraph explaining which design works better and why. Take comparison photos for extra evidence.
📄 Need this offline?
Print or save as PDF to use without internet — perfect for rural schools and low-data areas.