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Cleaner water at Elangeni The challenge was clear to Mr Brigden's class of 10 year-olds at Elangeni County Middle School, near Amersham in Buckinghamshire - to build a miniature water filter from simple materials and investigate its performance with different filtering materials: stones, sand, pebbles and gravel. Which combination would work best at cleaning the dirty water? |
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The 'dirty water' scale First the chidren agreed they had to devise a scale of 'dirtyness' that they could use to compare the water that came out of their filters. Eventually they agreed on a five-step scale, where 1 represented pure, clean water and 5 was unchanged, dirty water. |
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the filters Large empty plastic lemonade bottles were the bodies of the filters, with varying proportions of coarse sand, small and large pebbles making up the filtration medium, held in place with cotton muslin. The filters were held in clamp stands while the children collected 200ml of dirty water in a beaker. |
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Testing the filters The children poured their samples of dirty water into the filters and collected the filtered water in a clean beaker. Every 5 minutes they decided what the scale reading was and wrote down the volume that came through, then discarded the sample and waited for the next one. Presenting
the results
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Discussing the investigation After everyone had drawn their graphs they talked about which filtering materials worked best. The children generally agreed that sand made the water cleanest, but that the more sand there was in the filter the less easily the water came through - one group collected hardly a drop! |
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