I live and hike mostly in the Olympic Mountains. Sometimes I drink from streams that I know don't pass through commonly traveled areas. one of my friends commonly does that. We have never been sick from that. I carry coffee filters but if the water is crystal clear I don't even bother with them. I almost always is. Typically coffee filters are made up of filaments approximately 20 micrometres wide, which allow particles through that are less than approximately 10 to 15 micrometres. So it is far from perfect. What do you do? Boil, filter with a real filter? Drink directly from the stream if you know the source and feel safe about it? Ever been sick from drinking wilderness water?
I grew up decades ago hiking in the Cascade Mountains and no one ever considered ever filtering or boiling the water then. Maybe things have changed.