Check out this site
http://www.hollowtop.com/hopsstore_html/water_purification.htm

... and go down a few inches to where they talk about " The best form of iodine for water purification seems to be USP-grade resublimed iodine crystals". They talk about it being good for Giardia-infested water, but don't mention Cryptosporum that I saw, although I didn't go through the whole thing.

I remembered this from a video on survival... Woods something?

Sue