Spark tried this to show how water gets cleaned as it gets filtered through layers of the earth. This filter is not to make drinking water.
First he took a pop bottle and cut the bottom off. Into the top part of the bottle he put a layer of fiberfill batting.
Next he put a layer of charcoal. He used smashed charcoal that would be used for grilling. We thought that maybe fish tank charcoal would have worked better but this was the frugal route.
Next into the bottle went a few scoops of sand.
On top of the sand a handful of rocks.
First he tried water colored with red food coloring. Since I never color frosting, or anything with food coloring, all we had was some very old red paste food coloring that wasn't in it's prime.
The second time he put through a glass of blue water colored with a large amount of tempera paint.
Lastly, he tried muddy water from the garden. Yes, he has a different shirt on, he changes clothes an insane amount of times a day.
The one that worked the best was the blue tempera paint. While it didn't get it clear it did take a lot of the color out of it, it had a rather purple hue to it.
Dad pointed out though that if you eat something blue, like an raspberry icy, it does sometimes come out of you rather green the next day. If our bodies aren't able to filter blue perhaps we were asking to much of our little contraption here. By the time he tried the mud from the garden I think the filter had to much other color in it so while it did filter the dirt, the water came out the same purple color.