First, thanks to everyone for providing such good discussion around the article. Reading comments is what I enjoy the most about writing. Second, I want to address a few recurring themes in the commentary:
VIRUSES. It is true that the Katadyn filter inside the H2O Amigo does not offer virus protection. It is also true that the incidence of backcountry water-acquired illness due to viruses in the USA is unknown. There is not sufficient scientific data exploring how often viruses make people sick in the backcountry. However, even if there was such data, it would invariably be limited to specific geographic regions. This is because the types and quantities of contaminants in a waterway are dependent on land use patterns. Waterways downstream of population-dense communities are more likely to contain traces of human waste and therefore to contain viruses that make people sick. Waterways near areas with spare human population or are upstream of large communities are less likely to contain viruses.
When discussing backcountry water treatment, various technologies shouldn't be thought of as "better" or "worse" based on the absolute number or type of contaminants filtered, destroyed, or otherwise rendered harmless. Performance metrics aside, a water treatment technology is only as good as where it is planning to be used. For instance, a technology that does not offer coverage for viruses might be a bad choice for thru-hiking the Potomac Heritage Trail, which passes by a large number of densely populated areas and ends in Washington, DC. On the other hand, a technology that covers bacteria and parasites, but not viruses, is perfectly acceptable for hikes in sparsely populated areas.
WHY I CHOSE A DISCONTINUED PRODUCT: An area of interest of mine has always been low tech vs high tech in the backcountry. This article was thus an extension of this curiosity, where the H2O Amigo was the the best representative of the gravity filter concept, even though it has been discontinued (and perhaps making a comeback!?) My assumption was that since we, the readers of BPL, value ingenuity and ease of at-home modification and since the H2O Amigo can be made at home for low cost, this article was relevant.