/diy/ - Do It Yourself

Looking to make cheap air and water filters. Has anyone ever made purifying products from activated carbon? I want to make an air filter and a water filter, mostly for dust and pollen. I saw all I needed was a box fan and hepa or other filters for the air filter, and a carbon layer for smells (that I can make with activated charcoal), any good suggested ones for an amerifat? I think I need a pollen and dust one, are they as simple as pleating up a specialty fabric? Thanks!