Forward osmosis systems could potentially remove chemical contaminants. See http://www.247water.org/. They advertise it as working on contaminated water.

Basically, they have a sugar/salt syrup on one side of a membrane. Dirty water goes on the other side. Osmotic pressure pushes H2O from the dirty side to the clean side.

Never used it myself but thought it might be worth having a couple of the emergency use versions in a kit.