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Foraged filters

Search your surroundings and use natural materials to clean up your water source.
Plan a session with this activity

You will need

  • Paper cups
  • Access to water
  • Natural materials (for example, leaves, moss, twigs, feathers)
  • Container to hold water such as a bucket

Before you begin

  • Make sure you’ve risk assessed your meeting, and also have a COVID-19 safe risk assessment that’s been agreed by your line manager. You can check out more detailed guidance here

Safety checklist

Use the Safety checklist to help you plan and risk assess your activity.  Additional coronavirus-related controls to think about may include: 

  • Make sure that everyone knows the plan for dropping young people off (and picking them up again).
  • Set up a hand washing station that you can use throughout the session.
  • Think about how you’ll control interaction with people outside of your group.

Find your filters

  1. The person leading the activity should set some boundaries and limits so everyone knows where they can go during the activity.

  2. Everyone should spend up to 10 minutes searching for natural materials to use in their water filter. They should experiment and choose anything they think will help filter out dirt from the water, but they shouldn’t take anything from living plants.
  1. While they’re searching, the person leading the activity should fill a container with water. They should add a small amount of dirt and debris to the water to create some dirty water and set it aside.

  2. Once everyone’s finished collecting their materials they should take two paper cups and a pen, pencil, or stick.
  1. Everyone should poke a hole in the bottom of one of their cups using a pen, pencil, or stick.
  2. Everyone should layer the natural materials they collected (such as small stones, moss, and leaves) in the cup with the hole in to create a filter. They should experiment with different amounts of each material and their positions in the cup.

  3. Meanwhile, the person leading the activity should transfer the dirty water they made in step three into enough cups for everyone to have one each. They should leave a cup of dirty water two metres away from each person.

  4. Once the person leading the activity has moved away, everyone should take the cup of dirty water. They should hold the water filter cup above the other cup, and slowly pour the dirty water into the filter cup. A good filter should remove all the visible dirt and debris, but no one should drink the filtered water.

  5. Everyone should pour the water through a few times to see if they can remove even more dirt. They should try to perfect their filter each time, until it works as well as possible. It’s still not safe to drink the filtered water.

  6. As people are filtering their water, the person leading the activity should remind them that it’s not just the dirt that you can see in the water that might be bad for you: bugs, bacteria and viruses can all hide in water and make people very unwell.

  7. To make the water safe to try, someone should heat the water to a rolling boil, then boil it for at least five minutes.


This activity was all about valuing the outdoors and trying new things. Do people usually filter their water before they drink it? Some people may have a water filter at home to make their water taste nicer, but in the UK people usually have water that’s safe to drink in their homes. Did people’s filters work better than they expected? What outdoor materials were the most effective?

This was a fun experiment, but nearly one billion people around the world don’t have access to clean water. How do people think it affects their lives? People could think about using dirty water for drinking, cleaning, and washing their hands. How could people help? They could check out Scouts for Sustainable Development Goals for inspiration and ideas.


Outdoor activities

You must have permission to use the location. Always check the weather forecast and inform parents and carers of any change in venue.

All activities must be safely managed. Do a risk assessment and take appropriate steps to reduce risk. Always get approval for the activity and have suitable supervision and an InTouch process.

Make it accessible

All Scout activities should be inclusive and accessible.