Most gravity filters with a pore size of 0.2 microns. You set it and forget it. Let gravity do the work for you so you can multi-task, or just rest. Get one with a flexible bag and hose for about $85usd and it can roll up nice and compact. MSR Gravity Filter.

When you're starving and exhausted after a long day the last thing I want to do is pump water through a filter.

For backup, boil water or use chemical filtration. But I hear chemical filtration doesn't work so well in lower temps, like below 60F. Like it takes much longer to work, 30-40 minutes or so.

Also, I have not seen studies on how UV works on cysts, which is another thing you have to worry about. You ingest a cyst, the thing hatches, and makes you sick. Giardia won't normally kill you if you drink enough water, but you will wish you were dead. I've had it.