Dick Wix wrote: >>> First Need once supplied a "coloring dye" to check their filters... I don't know if it was only food coloring or not... I have not seen anything like this from other filter companies, ie MSR, PUR, SweetWater, Katahdin, Timberline, etc... <<< Actually First Need supplied the dye so you could "mark" the bottle with clean water. It had nothing to do with the filter. Tellydude