The best water purifier for general carry is Iodine crystals. Carry them in a 35mm can, add water, shake and pour into the canteen. They last, like forever. But, because of drug manufacturing freaks, I can’t find anybody still selling Iodine crystals. Any ideas? JWR’s Reply: Unfortunately I don’t know any sources. Sadly, most of the hobbyist chemical supply houses are a thing of the past, along with true hobbyist electronics stores. Perhaps someone reading this blog knows a good source for Iodine crystals. The iodine crystal method works well. A few large crystals will practically last a lifetime. However, …