[nine_k]

It's chemically inert, but has a very fine porous structure (thus 'activated'), so it works as a mechanical filter that adsorbs anything large enough, like bacteria and even very large molecules.

[fsck--off]

Activated carbon, also known as activated charcoal, was the useful ingredient in "universal antidotes". Although the mixture (see link) is no longer used, activated charcoal still is.

http://www.medilexicon.com/medicaldictionary.php?t=4805

[oasisbob]

It's chemically inert [...] so it works as a mechanical filter that adsorbs [...]

Because adsorption is a consequence of surface energy and weak bonding, I believe it's considered to be a chemical process, not a mechanical one.

[nine_k]

Right, the distinction is fine here.

Adsorption is due to weak bonds that form between molecules of a surface and a fluid. AFAIK this bond is not a 'new' chemical bond since it does not break / replace existing chemical bonds in both the adsorbed molecule and surface molecules.

Rather, in the case of carbon at least, the 'bonds' are the van der Waals forces.