I bought some pure iodine (well 99.8%) for water treatment. I realise that here in Aus (as well as se asia) our soils are depleted of iodine - so iodine for water treatment when needed should be a win win. So far I've never treated water (the luxury of being in isolated locations); but I want that ability to and not have to rely on boiling. Here's what I bought. It isn't the usual form of iodine that is used for water treatment, so I don't actually know how much is needed. If anyone knows, or any other hints or tips, I'd be thankful. I did do a search here, and there was talk about chrystals, which is actually a different form. The stuff I've bought is just iodine that's been prilled. However I did learn enough from here to confirm it is a good idea. One of the other options is chlorine (bleach). I do have a tiny battery driven gizmo somewhere (well, I haven't seen it for years) that I assume gets chlorine out of salt. I like the idea of iodine though.