Cleaning up water – looking at filtering

Today we are looking at filtering and how it can be used to clean dirty water.


How to filter water

What you need:

Dirty water ( or mud and clean water )

A funnel

Coffee filter/paper towel/muslin

An empty bottle


Place your filter into the funnel and pour the water through slowly.


Is the water cleaner?

Can you see the solids trapped by the filter?


There are many different ways you could construct this investigation. You could try just one filter and talk about how it traps the big bits of mud and dirt but smaller particles pass through, or you could compare 2 or 3 different types of filters to see what happens.

Is kitchen roll better than a coffee filter, would just a sieve work?

You could also work in stages, so try a colander, then a sieve and then a paper towel. Each stage should trap smaller and smaller particles.

The Science Bit

A filter is a porous material which a liquid can be passed though to separate the liquid from solids suspended in it.

We also have this post where we filtered toys.

Extension Ideas

Try filtering potions using a sieve and colander.

Can you filter water using sand and stones?


Suitable for Key stage 2 Science

Properties and Changes of Materials

Use knowledge of solids, liquids and gases to decide how mixtures might be separated, including through filtering, sieving and evaporating.



There are 11 comments

  1. Ticia

    We did that once too and it’s amazing how much gets filtered out and how gross that water still is. I think yours was more easily visble, we have very clay like dirt, so it didn’t quite dissolve right.
    Thanks for linking up to Science Sunday!

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