UV water sterilization is best used in municipal or installed units, I sure wouldn't trust a UV sterilization unit for backcountry water.

and yes, froze, all the other readily available portable systems good enough to meet EPA 'purifier' standards rely on iodine like the Exstream you mention.

I guess you could bring along a reverse osmosis system, but that's not really practical. Or maybe a steam still, you could make booze out of corn pilfered from farmers' fields on layover days...

The First Need is the only portable, EPA certified purifier that is mechanical only and doesn't require chemicals. iodine is dangerous with repeated exposure, limiting the Exstream bottle system for long term use.

I wouldn't rely on a UV device for backpacking water in the third world. better to have a field cleanable filter like an MSR or the large metal-bodied Katydin in conjunction with a chlorine hydroxide delivery system, or use a First Need purifier with options for replacement filters en route for extended trips.