We used to filter every drop. But on long travel days with long portages, there would never seem to be nearly enough water. So one particularly long and hot day I weighed the miniscule chance of stomach trouble vs. the 100 percent chance of dehydration, dipped my cup in the middle part of the lake, drank about 10 gallons ... and a new philosophy was born. We still filter (and have found a gravity fed filter to be the easiest), but I drink from the deep as often as not.

-- kypaddler