I recently came across (via a Facebook post) an article about Lifestraw, a device for making biologically contaminated water safe to drink. The marketing and publicity around this product seems exclusively geared towards the third world, as a way of preventing diarrhea-causing infections, which are the world's #1 cause of death. One Lifestraw can supposedly filter enough water for one person for one year, before the filtering capacity diminishes. Such filtration removes bacteria, viruses, protists, and just about any other form of biological contamination. Presumably, it cannot remove salt, chemical pollution, or other substances which are truly soluble, since filters...