Many will remove suspended particles or chemicals, but not dissolved ones.

This is probably the best there is, but even it is not going to remove dissolved chemicals:

http://www.lifesaversystems.com/techinfo.html

But at $150 it's pricey.

A good and cheaper one ($60) is (although I wish it had a carbon filter in addition to ):

http://www.walmart.com/ip/Sawyer-Water-P...4#ProductDetail

It filters to .02 microns so it removes viruses as well.

Do they make portable reverse osmosis systems?