We have recently been learning about water pollution and decided to build a water filter to see how clean we can make polluted water, using an easy homemade filter. We did this project in groups and were given the apparatus needed. We needed gravel, coarse sand, fine sand and a 2 litre bottle which was cut in half. We also had a choice to bring activated charcoal and cottonwool. My group did use activated charcoal and cottonwool and we also added rice as our 'cheat' item. The result was that all our filters filtered out the insoluble substances like twigs and leaves. Some worked better than others and had clearer water but none of them were 100% clean. We would still have to boil the water to make it safe.