Iodine should not be used by any of the following:

• those on thyroid medication,
• lithium medication,
• pregnant women,
• those with allergies to iodine or shellfish, or
• people with active thyroid disease.

It appears safe for short term use (3 month) for others.

Add the recommended amount, mix it well in the water and let it stand for at least 30 minutes at 70 degrees, longer when the water is colder. You can add a small amount of vitamin C (50 mg.) or other powdered drink flavorings to the water to improve the taste. There are also commercially available iodine tablets in sporting goods or outdoor supply stores. Use them according to directions. Once any iodine bottles are opened, they should be used within the specified time frame.

Iodine has been shown to be more effective than chlorine-based treatments in inactivating Giardia cysts.