I'd also like to point out, as one of the "senior" generation, that the current backcountry practices of treating water didn't start until the late 1970's, when a lot of folk started getting giardiasis or similar illnesses after backcountry trips. Studies, especially by state fish and game departments, showed widespread giardia contamination in backcountry waters being spread by wildlife in the water (which most likely caught it from domestic animals or from humans not practicing proper sanitation). In other words, the idea of treating water didn't start out of the blue because some commercial outfits were exploiting the idea! In fact, filters for treating backcountry water didn't show up until several years after the above studies were first publicized. Back then it was a choice between iodine (which in my case resulted in a horrible allergic reaction!), chlorine bleach or boiling. It has since been proven that iodine and chlorine bleach (as opposed to chlorine dioxide) are not very effective in killing protozoan cysts.

The standard water test is only for coliform bacteria, but that started increasing in backcountry sources at the same time! The coliform bacteria count is an indicator of how much the water is polluted. They can make you sick, too!