Our first filter had big rocks, then little rocks, then sand.
We tested our filter with water mixed with dirt, bark, dish washing liquid and oil.
We compared our dirty water with the filtered water and although it was a little cleaner it was still very dirty. It ran through the filter very quickly.
We then built a second filter - this time we used cotton balls, then stones and then sand. It took quite a while for anything to happen. Our video shows this clearly but you have to tip your head sideways because that's how it uploaded.
We then compared the unfiltered water with our two filtered examples. The cotton ball filter definitely worked the best. It took much longer for the dirty water to filter through and you could see all the dirt being trapped in the cotton wool. We talked about how the roots of plants work like filters and help absorb all the things in the water, cleaning it before it goes into the stream.
