Well, that's kinda misleading on First Need's part. Charcoal adsorbs organic chemical constituents in water (such as dye) but it has no effect on cysts or bacteria or viruses (unless it's been formed into a mechanical filter element, e.g., by sintering it into a porous block--IIRC Safewater Anywhere used to do this). The charcoal added to typical filter elements that have it is composed of loose granules that you can hear when shaking the filter element. Examples are Katadyn Hiker and MSR Sweetwater. This carbon will reduce organic chemials in water but is unlikely to eliminate them because you need a lot of charcoal and appropriately low flow rates for complete removal of organics. In typical filters, the job of removing biological constituents goes to the filter fabric, ceramic element, or other physical filter media such as the hollow fiber filters. And this is where the dye test cannot demonstrate filter failure. It simply isn't a valid test of filters not designed for 100% organics removal, which includes the majority of backpacking filters because dye isn't a substitute for sub-micron particles (as an analogue for bacteria).

I confess I have no idea what's inside a First Need cartridge or how it supposedly works. Has anybody cut one open to see what's inside? It would probably be a good choice for anyone suspecting pesticide contamination in water.

Cheers,

Rick

p.s. MSR has a simple vacuum test for the HyperFlow that can demonstrate the cartridge's condition in the field. It's a nice verification from a peace-of-mind standpoint. They've also corrected the flow issues that plagued it the first year.