Its cheap and a friend uses for his cresties egg box. Never heard of it before then though
reverse osmosis look it up on how things work you may have the thing you need to do it
You have so many options with these materials most all of these materials can be used as a filter. I am not sure how advanced you need to go with this or how you want to do this but I would set up a multistage system similar to a fish tank filter rap the charcoal in the gauze and layer the rest in the tube. You can go all out by making it a multistage system where it will go through the charcoal filter tubing then a chemical cleaning through the soda bottle then finally through a filter
cut the top of a bottle and the bottom and cover one bottom with gaus then put rocks and some cotton balls in between some of the rocks.
You have a good selection of materials to make a progressive filter. Divide your materials into 3 categories: 1. Filtering materials in order of effectiveness- rocks, kitty litter, vermiculite, sand, gauze, cotton paper towels, coffee filters, activated charcoal... etc. 2. Containers- soda bottles, plastic tubing. 3. Attaching materials- hot glue, duct tape. Now you have to put the materials into the soda bottles. Start with the rocks. Cut off the bottom of the bottle, put some gauze in the mouth of the bottle put a hole in the cap, and put in on the bottle. Now turn the bottle over and put in the rocks. This is stage 1 of your filter. Take another bottle with a hole in the cap. Cut off the bottom and duct tape this into the open end of the bottle to hold the rocks in during transport and to act as a funnel. Stage 2 is almost the same. This time use the kitty litter instead of the rocks. Stick the neck of the first stage into the open end of the second stage and use the duct tape to hold them together. Stage 3: Vermiculite Stage 4: Sand, but now you have to use the paper towel instead of the gauze because the sand can get through the gauze. Stage 5 is just the coffee filters Stage 6 is the activated charcoal and use the cotton in the neck to keep the charcoal in the bottle. The last stage should again use a coffee filter to get any bits of charcoal that may have escaped. If you duct tape each stage carefully to the next you will have a tall progressive filter. You pour in the polluted water at the top and you will have pretty well filtered water at the bottom.
