I just bought a new water filter for backpacking, an MSR Sweetwater, but I found the whole product category confusing and so I offer my brief research here in hopes that it is of service to someone else in a similar situation.

I had owned an MSR Miniworks for many years and ended up giving it to a friend going on a long trip, so I needed to replace it. Plus, it’s good to have a water filter as a part of an emergency kit, especially here in earthquake country.

The ‘water filter’ category actually includes both water ‘filters’ and water ‘purifiers.’ The distinction as far as I can tell is that purifiers remove viruses in addition to waterborne pathogens like giardia and crypto. Filters only remove giardia and the like. In North America we don’t have a problem (yet?) with viruses in the backcountry water, but in the developing world waterborne viruses are also a concern. I ended up getting a Sweetwater purifier — which is a Sweetwater filter plus some drops that kill viruses — because I plan to bring it on trips to the third world.

Most filters have some kind of ceramic material that you pump the dirty water through, although Steri-Pen makes a purifier that uses UV light; that means you have to be careful to zap all the water in your bottle and carry spare batteries. MSR also makes a purifier, the MIOX ($140).

In fact, to me, the MSR product portfolio for backpacking water filters is very confusing. Besides the MIOX, they have what I think of their ‘main’ product, the MSR Miniworks ($80), which weighs 16 oz. and is from my experience tough and field-maintainable. It has a ceramic and carbon filter that supposedly filters to 0.2 microns. But MSR also sells the Sweetwater (also about $80), which was a competing product until they bought the competitor.

The Sweetwater is lighter — 11 oz. versus the Miniwork’s 16 oz. — and also filters down to 0.2 microns. (The claims about filtering down to 0.2 microns sound good, but from my research the reality is a little more complicated and beyond me.)

The Sweetwater doesn’t attach directly to the top of a Nalgene bottle, like the Miniworks; instead, it has a hose with a Nalgene connector on it. From my kitchen sink tests, I think I prefer the Miniworks screw on style, but that just may be because of my prior experience with it.

But MSR also sells a new filter, the Hyperflow ($100) which only weighs 8 oz. (10 oz. with everything you need); it’s promising but seems fragile and unproven. It uses some new filtering technology that is supposed to be field-maintainable but you can’t let it freeze.

Katadyn also makes backpacking water filters, including the Hiker Pro ($80, 11 oz.), the Hiker ($65, 11 oz.) and the Vario ($72, 18 oz.).  The two Hiker models filter down to 0.3 microns, but I don’t think that in of itself is all that important.  I can’t tell the difference between the two Hiker models; I think it’s a matter of being field-maintainable or not.  I recently used a friend’s Hiker Pro — it has a two hose arrangement, like the Sweetwater — and it worked well.

There’s also the popular First Need XL purifier (16 oz.), but I don’t know anything about it.