I am having a hard time figuring out the differences between the various water purifiers. A good water filter will eliminate such nasty but fairly good-sized nasty characters as giardiasis, cryptosporidia and amoebas. Filter materials vary, but many employ a very fine-pore ceramic element or one made of fiberglass. For most hiking, canoeing and other outdoor activities in North America, a filter is sufficient.
Purifiers do more.
In addition to filtering water, a purifier goes an extra step to kill those things that are so tiny that they escape a filter's net. We're talking viruses, in most cases. Filters do so in most cases by sending water through an iodine-laced cartridge. They're designed primarily for international travel. A growing filter category consists of filters incorporated in a sports-type bottle.