The lake water in the BWCA looks clear, but that doesn't mean that there is nothing there to be filtered out. The ceramic filter cartridge (vario) pore size is smaller than the hiker's paper filter and will catch a lot of stuff (invisible, and nearly so, like some algaes) that the hiker will miss. There is nothing wrong with the varios in this respect.Took a group to BWCA in 2007. We had 3 Varios and 1 Hiker. All 3 of the Varios went south on us after about 10 gallons. Very disappointed. The water is crystal clear so that wasn't an issue.