This prepping and survival blog article reviews the use of iodine, in tablet or liquid form, in order to kill pathogens: bacteria, viruses, parasites.
As a method of water purification, any type of chemical disinfection is far from ideal. Commercial water purification, used to produce bottled water, often combines more than one method: micro-filtering, charcoal filtration, reverse osmosis, distillation, ozonation, etc. Municipal water supplies, in addition to using multiple methods of water purification, also use chlorination. They add small amounts of chlorine to the water as a final step to kill pathogens. Iodine is not generally used in commercial water purification.
For emergency water purification, iodine (tablets or liquid) has the advantage of being easy to store, easy to carry with you if you are camping or bugging out, and can be used without heat or electric power. However, heating the water to a full rolling boil for one minute is always better than any additive at killing pathogens. And distillation of the water is even better, since it both kills pathogens with heat and removes most contaminants by distillation.
This method of chemical disinfection is available as tablets (tetraglycine hydroperiodide) or a liquid (tincture of iodine 2% solution). I tested both options: Potable Aqua tablets and ordinary tincture of iodine.
The CDC has a good page on the use of iodine for chemical disinfection of water. They say:
“If water is extremely cold, less than 5° C (41° F), an attempt should be made to warm the water, and the recommended contact time (standing time between adding a chemical disinfectant to the water and drinking the water) should be increased to achieve reliable disinfection.”
This recommendation is true for all chemical disinfection methods (as far as I know). Chemical reactions typically proceed more slowly at lower temperatures. So if the water is cold (below 25 degrees Centigrade or 77 degrees Fahrenheit), the length of time required for the chemicals to react with the pathogens is longer. The rule of thumb is as follows:
“Allow the water to stand for 30 minutes before drinking when the water temperature is at least 25° C (77° F). Increase the standing time for colder water: e.g., for each 10° less than 25° C (77° F), allow the water to stand for double the time before drinking it.” [CDC]
A 10 degree drop in temperature by the Centigrade scale is equivalent to an 18 degree drop on the Fahrenheit scale. So double the standing time for every 18 degree drop in temperature:
77° F = 30 minutes
59° F = 60 minutes
41° F = 90 minutes
Anything colder than 41 degrees should be warmed before using any chemical disinfection method.
I tested Potable Aqua with PA Plus from Coleman. There are two small glass bottles. The vial labeled ‘Potable Aqua’ contains the iodine chemical. The bottle labeled ‘PA Plus’ contains ascorbic acid, which is simply vitamin C. You absolutely must NOT add the two tablets to the water at the same time. The ascorbic acid deactivates the iodine, making it ineffective. FIRST, add the iodine tablets (a dark violet color) to the water, then wait the requisite time of 30 minutes or more. Only after the iodine has disinfected the water can you add the ascorbic acid (PA Plus) to take away the iodine taste.
The directions say to use 2 tablets for 1 liter or 1 quart of water. The difference in volume between a quart and a liter is too small to make a difference; that is why they say that. I used one tablet for a half liter bottle of water. The tablet should turn the water a light brown color.
There is a clever tip in the directions. Let the tablets dissolve, which takes about 5 minutes. Then loosen the cap of the container and shake, so that the iodine infused water gets on the inside of the cap and on the threads of the bottle. Then wait 30 minutes (technically, 25 more minutes). This makes certain that the water at the top of the container and on the threads is also disinfected. Otherwise, when you drink from the bottle, you might have some contamination from around the top of the bottle.
AFTER adding the iodine tablets AND waiting the required length of time, you can then add the ascorbic acid tablets. The PA Plus tablet (ascorbic acid) does not need to dissolve completely to be effective. The water quickly changes, in about 5 minutes or less, from a brownish iodine color to clear. You can then drink the water. The PA Plus really was effective at taking away the iodine taste.
Tincture of Iodine
I also tested 2% tincture of iodine solution. The CDC recommends 5 drops (one fourth of one milliliter) per quart or liter of water. I found this dosage difficult to measure. A droplet does not have a uniform size. The water did not change color, but it had a strong iodine smell. After 30 minutes, I dropped in an ordinary vitamin C tablet containing ascorbic acid. Be advised that some vitamin C tablets are not ascorbic acid, but some other form of the vitamin. The acid form works to deactivate the iodine and remove its offensive smell and taste. Other forms of vitamin C might not.
The ordinary vitamin C tablet was ascorbic acid, but it did not dissolve quickly like the PA Plus tablet. The water was left with an off-taste.
I only used tap water for this test. But if it had been contaminated water, I’m really not sure if the tincture of iodine was the right dosage. I would much prefer to have the tablets with the PA Plus. The tablets are the preferred form of iodine, in my opinion, since the dosage is easy to measure: one tablet per half liter (one pint). The ascorbic acid is very useful, since iodine has a nasty metallic taste otherwise.
Pros and Cons
On the con side, iodine in any form is limited in its ability to kill certain pathogens:
“Cryptosporidium (a parasite that can cause diarrhea) and other coccidian parasites (e.g., Cyclospora, Toxoplasma) might not be killed by this method.” [CDC]
If the water is cloudy, any chemical disinfection may be less effective. You can reduce the cloudiness of water by allowing it to stand for a couple of hours, or by straining through a coffee filter or clean cotton cloth.
Also a negative is the fact that iodine, in high enough dosage, is lethal. See the CDC warning on this point.
On the pro side, the treatment of the water with iodine tablets is easy to do, and requires no heat or power. Using ascorbic acid AFTER the water is disinfected with the iodine removes the bad taste that would otherwise make iodine a much less palatable option. In my test of Potable Aqua with PA Plus, there was no iodine taste in the water. There is perhaps a very slight taste difference between treated water and plain tap water, but it is difficult to discern. The treated water is pleasant to drink. By comparison, the water purification filter that I tested a while ago, LifeStraw, gave the water a strong plastic taste.
Boiling water is preferable to iodine, since boiling is more effective at killing a wider range of pathogens. But if you are camping, bugging out, or traveling, and cannot boil water, iodine is a convenient and useful option.