Tincture of iodine is 1-5% Iodine, 1-5% Sodium Iodide in an alcoholic solution with water.

The free iodine content is what is used to purify water. This is compared to providone iodine which contains 10% iodine. The concentration only means that less is used to puritfy the same amount of water.

Actually, iodine is food for the thyroid. The iodine is required to produce thyroxine. In areas where there is a lack of iodine, there is a large incidence of goitre and hypothyroidism in infants which leads to mental retardation, hence the introduction of iodized salt into diet. However chronic excess intake of iodine will lead to iodism - headaches, salivation, skin rash,weakness etc.

An amount of 8mg of iodine per liter is required for purification. Ok you chem guys help me out here. How many drops of providone iodine or tincture of iodine will give 8mg per liter ?

As for your wife's thyroid condtion, I can surmise that she is hypothyroid because she is on synthroid. Hypothyroidism may be because of thyroid infection, autoimmune damage, surgery, radioiodine therapy etc. The iodine on short term use will not cause any untoward damage. The patient already is on thyroxine replacement which means that there is already very little functioning thyroid tissue.

In general, short term use is OK. Not for more that a few weeks definately. Of course if you have other alternatives available, use them e.g. chlorine based, boiling, filtering etc.

Of course, consult your own physician / endocrinologist for further advice with regards to her exact thyroid condition, this information should not be used to diagnose, treat or form the basis for instituting any treatment, procedure or otherwise without first consulting your own physician.