After a few weeks of using iodine to disinfect my water (only on weekends), I broke out in a really horrible all-over rash with deep lesions (lichen planus), that left permanent scars. I was so sensitized to iodine that I still cannot eat seafood or anything made with iodized salt, which causes lots of problems, not just socially (since most people and restaurants cook with iodized salt) but also medically.

Iodine treatment for water is definitely contraindicated for pregnant women and children, which should tell you something. It's also a no-no for anyone who may have thyroid issues.

Plus iodine has been shown to be ineffective against cryptosporidium, which is becoming an increasing problem in many areas.

The CDC recommends iodine for water purification only for brief emergency use.