Thanks for the information. Since I rarely filter or purify any of my water, I guess I have not over-dosed yet! The water quality is excellent in most of the places I backpack. The Katadyn tabs are so nice, easy and light weight, I am glad they are still considered OK. The iodine habit is a hold-over from the days before chlorine tabs. Many times it is a matter of availability - often I am in places where the stores only carry iodine.

Another question? Do the tabs deteriorate with time? I noticed that iodine tabs seem to disintigrate if several years old. Are the chlorine tabs subject to deterioration?