Just saw an article on this in the Denver Post newspaper (available online: http://www.denverpost.com/search/ci_4467390 )

Water filtration for about a $3.00 manufacturing cost. The Post article says it is not effective against Giardia though <img src="/images/graemlins/frown.gif" alt="" />

Still, it might turn out to be a good device to have for emergencies.

Company website: http://www.lifestraw.com/en/low/low.asp