I suppose that certain alcohols could evaporate out. Sometimes you can
add something to the impure water source to help absorb impurities. Mud
or seaweed is sometimes added, in the hope that it will help absorb
impurities. I'd imagine that saturated fabrics or paper might also
absorb certain kinds of impurities.
"It is fashionable to wax apocalyptic about the
threat to humanity posed by the AIDS virus, 'mad cow'
disease, and many others, but I think a case can be
made that faith is one of the world's great evils,
comparable to the smallpox virus but harder to
eradicate." -- Richard Dawkins