In regard to iodine, I used iodine exclusively during 13 treks (from 3 to 29 days) over a 2 year period. Probably drinking 2-3 liters a day at minimum. (4 drops iodine per liter) I was treating very questionable water (in a developing country with poor sanitation). I got stomach sickness once while on trek, although I attribute that particular sickness to some super-sketch food, not the water. So, that is my experience. Now I use a water filter just for the difference in taste.