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The standard Brita pitcher filter is a mix of granular activated carbon (from coconuts), and the ion exchange resin you talk about.

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Thanks, I didn't know that! What does the activated carbon do?

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.

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

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.

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.

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