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Iodine or iodine tablets to purify drinking water: Here we explain how to use iodine tablets or liquid iodine as a drinking water disinfectant, and we cite the limitations of this method.
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This article series outlines methods to purify or sanitize drinking water in an emergency following a disaster such as an earthquake, flood, or hurricane.
See Filters for Drinking Water Purification for a discussion of portable and emergency water filters that are designed to purify drinking water, including portable ceramic water filters, silver ceramic filters, magnetic (bogus) water purifiers, paper and polypropylene water filters, etc.
See DRINKING WATER PURIFICATION for a discussion of various methods used to purify emergency drinking water. A companion article, DRINKING WATER - EMERGENCY SOURCES,describes possible sources of drinking water that may be useful in emergency conditions.
Flood Response Checklist lists key actions you should take after building flooding to minimize mold damage, and includes some safety warnings. Before entering a building that has been affected by a disaster such as fire, earthquake, or flood, See BUILDING ENTRY for DAMAGE ASSESSMENT for some safety warnings for occupants, building owners, or volunteers who may find themselves indoors in a disaster area and without immediate assistance from rescue workers or other experts.
Iodine and bleach (chlorine or sodium hypochlorite) are the two common ways to sterilize water chemically to address bacterial contaminants. Iodine tablets have been shown to be effective against Giardia muris but iodine tablets are not effective against Cryptosporidium species.
How to use water purification tablets:
Paraphrasing the Potable Aqua® instructions: Two tablets are added to a quart of water (or to 1 liter of water) to be treated. The water plus tablets is left in a loosely-capped bottle or similar container, loose enough to allow some leakage. Allow this combination to stand for five minutes, then shake the container to moisten the threads on the container and its cap. Then tighten the cap and allow the water plus tablets to sit for 30 minutes before drinking.
Watch out: Cryptosporidium cysts might survive a typical chlorine disinfection process (such as at a municipal water treatment plant).
For this reason some municipalities where Cryptosporidium cysts are a concern add a water treatment step using chlorine dioxide. Others may use a combination of UV light and chlorine in the water treatment procedure. This treatment is also available to hikers, travelers, and for emergency water supply use.
Katadyn® water purification tablets are sold as Micropur MP1. Quoting from Katadyn's product literature:
See FILTERS for Drinking Water Purification for some alternative approaches to water purification that can handle cryptosporidium cysts.
Guide to Using Tinctures of Iodine to Disinfect Drinking Water
Also see Wait Time & Water Temperature When Adding a Disinfectant - Before Drinking the Water where we provide more details about how to use iodine as a disinfectant.
[OPINION] In an emergency if you have nothing else, no way to boil water, no ceramic filter, but you have iodine, use it. But beware that iodine is not fully effective as a water sterilization method and be sure to see the allergic reaction warnings just above.
Using Lugol's Solution for Water Disinfection?
Reader question: I looked at the article about water sterilization from the link that you sent me and I saw no mention of Lugol's iodine as a sterilizing agent. Am I missing an article? I did see the post about using chlorine to kill Giardia cysts (GIARDIA in DRINKING WATER) where you cite:
Is that 10 parts of chlorine to one part of Water? Is that the dilution of chlorine that one woul buy in a container of Chlorox? Thanks - G.B. / S.R. 5/30/2013
Watch out: The Manci citation specifies 10 milligrams of chlorine per liter of water: That is nowhere near a 10:1 ratio. Confusion about proper dilutions of disinfectants can lead to dangerous drinking water.
Lugol's Solution or Lugol's Iodine I2KI
Indeed chlorine (bleach), iodine, and permanganate all have been widely used in water treatment and disinfection systems. We have written about iodine as a water disinfectant and I've used various formulations including Lugol's iodine in the lab as a stain, but I've not written not specifically iodine mixed with potassium iodide - Lugol's solution - as a water disinfectant. (Synonymns I2KI (iodine-potassium iodide); Markodine, Strong solution (Systemic); and Aqueous Iodine Solution BCP).
I've read that while there is a historic use as a water disinfectant including following Chernobyl (where it had a second purpose) the mix can also be toxic if drunk or ingested at concentrations of 2% & above. The Wikipedia article adds "The lethal dose of free iodine for an adult human of 2 to 3 grams (2000-3000 mg) free iodine represents 40 to 60 mL (less than 2 fluid ounces) of 5% Lugol's solution. I'll add these notes to our iodine discussion found at along with some useful citations  about iodine as a disinfectant in articles citing the preparation and use of Lugol's solution.
Because there can be health problems from unsupervised consumpation of iodine, and lacking expert sources that argue otherwise, I am not competent to recommend regular use of Lugol's solution as a general purpose water disinfectant in any of the forms discussed. Here is what Backer & Hollowell say about using iodine (but not specifically Lugol's solution) to disinfect water:
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