Iodine tablets– One tablet added to a quart releases 8 ppm (parts per million) of iodine. Two tablets are used for turbid water. Wait 15 minutes after adding tablets, 30 minutes if the water is cold. The shelf life of the tablets is 3-5 years. Deterioration is evidenced by a change in the tablet color; metallic gray is acceptable, light yellow double the dose, and reddish brown discard. The formation of a precipitate is acceptable. If there is starch in the water from potatoes, corn or rice the water will turn a blue color. The blue colored water is harmless and is acceptable to drink. Iodine tablets are not effective against Cryptosporidium and according to some experts ineffective against Guardia. The iodine tablets leave a strong taste in the water.
Carrying iodine for water purification is a lightweight solution for those in temporary need of clean drinking water. Kits are available in camping stores that include an iodine pill and a second flavored pill (vitamin C or ascorbic acid) that will remove the iodine taste from the water after it has been disinfected. The addition of vitamin C, in the form of a pill or in flavored drink powders, precipitates much of the iodine out of solution. It should not be added until the iodine has had sufficient time to work. This means a minimum of 30 minutes in clear, warm water, but is considerably longer if the water is turbid or cold.
The same general factors apply if you use the crystalline Iodine, except that the shelf life is indefinite as long as it is kept in the crystalline form.
Warning – Pregnant or nursing women or persons with thyroid problems should not drink water disinfected with Iodine.
I personally do not use iodine or chlorine except in an emergency, today there are much better choices available. I will cover some of these options in future posts.