After reading the previous posts, here's my two cents.
I have both the "Polar Pure" iodine treatment, and the "MSR Water Works" filter. In real world practice, if it comes out of a tap, or other trusted source, it goes through the filter. If it's standing, or flowing, or whatever, e.g. unknown source, it gets chem. treatment, then run through the filter. Some might call this over-kill, but where my health is concerned, I figure I can't be too safe. Treating the water, then filtering it takes more time than filtering alone, but saving one case of the trots is well worth it.

Troy