I'm like many others here, never filtered my water in 40 years of tripping until ...  Until 3 years ago when my wife and I did a trip, as we have so many times before, in Algonquin.  I did what I had been doing forever, namely going out into the middle of the lake and taking what I needed.  We also took water a couple of times from an artesian well and now that I think about it, that might have been the problem.  But, in any case, my wife came home with Giardia.  Somehow I didn't contract it, but it was no fun for her.  Since then we've gone with a filter.  I use the Katadyn Pocket Water Filter which is an extremely well built and well engineered piece of kit.  Its easy to repair in the field if necessary but its built like a tank so it's hard to imagine what could break.  Pumping water for one or two people is really no big deal certainly no more effort than paddling out to the middle of a lake to get it.  And the peace of mind is worth it.  Having Giardia symptoms for the last week of a canoe trip would be a colossal bummer.