When I'm out on a big deep lake, I drink right from it and never had any issues.

Since I'm always solo, and duct tape won't fix what bad water can bring, I use a filter because I get water from the shore wherever I camp.

  My immune system is pretty strong but I don't discount getting sick, so I have that gravity filter.

Like almost everything you encounter on a wilderness trip, you have to do what makes the most sense to you.

I've had my share of injuries BUT having the trots for days would be worse than all of them.  :'( :P