I just read Cody Lundin's new book, and he recommended using tincture of iodine (what does "tincture" mean?) for purifying water.

My wife has thyroid problem and is on a steady diet of 125mg of synthroid every day. Would there be any problem with her having water purified with iodine? Does this apply just to "tincture" or does this include ALL iodine-base water treatments?

If there is a problem, should I use bleach instead for her? What is the theory here? What does iodine have to do with the thyroid?

Thanks in advance...