Thanks for the information, everyone. Have looked up most everything listed here.

I'm between two choices now:

Untreated for springs, and use Aquamira drops (after my iodine is used up) for questionable water sources.

Or this gizmo: Sawyer In-line Water Filter
It claims to not need replacement filters, due to it being some kind of holey plastic instead of a fabric or ceramic. Does anyone here have experience with it? I like the idea of not having to purchase filters, and it's fairly cheap.

A bit bulkier, but if it actually works it would save some money in the long run, since it can be used by two people easier than consumable products.