Plain charcoal works okay, but activated charcoal is the gold standard. Activation is just a fancy word for "make it even more porous." You do this by grinding the charcoal into a fine powder, then mixing it with a solution of calcium chloride (from pool supply stores) or lemon juice.
Boil the mixture for about 30 minutes, then rinse it with clean water until the pH is neutral. Dry it in the sun. The result is a powder that has a surface area the size of a football field per gram. No joke—it’s that porous.
DIY Charcoal Water Filter Instructions
Building Your Filter
Don’t expect to run river water through a sock full of this stuff. For a DIY water filter, use a plastic bottle cut in half. Layer in: small rocks, then sand, then a thick layer of your charcoal, then more sand, and a coffee filter on top.
Pour in murky water and watch it drip out clearish. It won’t remove viruses (you’ll need to boil the end result), but it will knock out heavy metals, chlorine, and bad tastes. It’s like having a Brita filter that you built from a tin can, which is rad.
