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.htmlBut 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#ProductDetailIt filters to .02 microns so it removes viruses as well.
Do they make portable reverse osmosis systems?