I have an MSR filter (the larger one, can't remember the name right now). I have filtered water from high mountain lakes and streams with no problems at all. This filter is supposed to get out all contaminants, including Giardia. $80 for the filter, but a good investment IMO. I currently have a set-up in my daypack that allows me to pump water directly from the filter into my Camel Back without taking the Camel Back out of my day pack. I just bring out the filter, hook upa hose, and start filtering.