Thanks everyone for your insightful and funny responses. I wanted to make sure there wasn't some technique I was missing.
For my approach in Appalachian mountain wilderness areas, boiling water or melting snow would generally work well because I have a campfire in the evenings. I don't like chemicals because of the taste, and they require a 4 hr treatment time for protozoa at low temperatures, which I estimate is the most likely pathogen. If I can wait 4 hrs for water, I'm in camp and could easily just boil some water.
I'll probably just stick to what has worked for me in the past in the winter: drinking straight from carefully selected sources. I do like to filter when possible just to be safe, since it's only a 4 oz weight penalty. But, I'll save that precaution for the 3 seasons.