I have a MSR Miniworks ceramic water filter I've used backpacking for 3 years. This is the same water purifier issued to the USMC. This thing works GREAT! You can put even put the tube in beer or soda and get straight H2o when you use it. No impurities. If you're worried about contaminated (meaning in a chem/bio war scenario) water, I'm not too sure what it would do, but the Marines are told to only drink bottled water, or in an emergency, filtered, boiled, and iodined water. You can see the website here:
[url]http://www.msrcorp.com/[/url]
It cost me about $65 a few years ago. Easy to clean too!