Thanks, Bob. I've always operated under much the same principles, but the more I read about backcountry water the more confused I get.
In my pre-UL days, I carried a PUR filter/purifier. I've been trying to learn how to effectively use chemical treatments and UV light; both, of course, have no "filter" in the system. That's made me wonder just how necessary it is to pre-filter water before treating it with, say, AquaMira or a Steripen. Believe it or not, it's been difficult to find clear statements about it.