Water Filtration Project: Make Your Own Water Filters ...
1 liter of water prepared in advance with soil and sand in it until it is thin but relatively opaque; 3 test tubes prepared with the water standards "A," "B" and "C" (C is filtered through some grass, B is filtered through a coffee filter, and A is filtered through 2 coffee filters with a paper towel in the middle) cotton balls; gauze squares