I have a Kataden Vaio filter for walking around (me and the best mate have the same gear so we keep a stock of spares between us which helps), thus far I am really happy with it. Some places I hunt have eitehr NO drinking water (as in NONE) or clean running water that is free of most nasties. I grew up drinking right out of the creeks here so anything I was going to catch I should have had now... :-)

When I run the filter I try to put the water through a "milbag filter" first though this is not always practical. I have milbags in my cars along with tablets as a back up to the system, the millbag will remove most solids and the tabs make it safe (though not nice) to drink.

back ups to the back ups with water, espectailly out here.