within the USA I have used the filters extensively and they work fine.

overseas, the ENEMY of all "systems" is good old-fashioned dirt. once you've got dirty water as your starting ingredient, all bets are off. filters clog fast and are a real hassle to clean (especially Katadyn's).

chemicals like bleach, iodine, chlorine all taste pretty bad in the water. nothing cancels out the taste. most people will not drink it once it tastes terrible, so the majority of people get dehydrated. have to admit that I was the most disciplined of the people in the various groups that I traveled with, and even I got sick of "chemical water" fairly quickly.

strain out the large gunk, and boil the water.
or buy pure.

cheers,
Pete