I've heard that iodine water treatment tablets can have negative side effects.

Is this true?

If so, what are some healthier alternatives?


4 Answers 4


Via WebMD

Large amounts or long-term use of iodine are possibly unsafe. Adults should avoid prolonged use of doses higher than 1100 mcg per day (the upper tolerable limit, UL) without proper medical supervision.

However I seriously question that 1100 mcg number because people in Northern Japan have been found to consume over 80,000 mcg per day due to a diet high in sealife (mainly seaweed) and they appear to be living just fine.

Pregnancy and breast-feeding: Iodine is likely safe when taken by mouth in recommended amounts. Do not take more than 1100 mcg of iodine per day if you are over 18 years old; do not take more than 900 mcg of iodine per day if you are 14 to 18 years old. Higher intake might cause thyroid problems. The topical product (2% solution) is likely safe for use on the skin.

Autoimmune thyroid disease: People with autoimmune thyroid disease may be especially sensitive to the harmful side effects of iodine.

It's clearly an issue if you are allergic to iodine.

If you already have a thyroid condition, too much iodine can complicate treatment.

Okay, so here goes:

Purification guidelines are 0.5 mg/L. Let's assume you need four liters per day (someone can comment a better guideline for water quantity, but I normally drink about four per day when hiking)

2 milligrams = 2000 micrograms. So yeah, that would exceed the 1100 UL dosage limit. However if you consider the people of northern Japan to be evidence that the real limit is much higher, then you are in no danger from this dosage.

A note on all of this: Everything I can find (CDC, webmd, etc) falls along the lines of "It's probably safe, but we're not sure and it may cause these issues".

You're extremely unlikely to manage to poison yourself unless you just nom the tablets (a couple thousand of them). Poisoning occurs in grams, several orders of magnitude more than what is used to purify water. To poison yourself, you'd need to consume ~2000L of iodine purified water in a short period, at which point iodine is no longer your primary concern.

  • 1
    I'd like to point out that on a typical hiking trip, you wouldn't be using iodine for "prolonged periods".
    – MBraedley
    Feb 21, 2012 at 15:11
  • "people in Northern Japan have been found to consume over 80,000 mcg per day due to a diet high in sealife (mainly seaweed) and they appear to be living just fine." - Not only fine but longer and healthier, that statement saying that iodine in large quantities is bad is just a hoax +1
    – Kyle
    Mar 29, 2016 at 13:34
  • This is from Use of Iodine for Water Disinfection: Iodine Toxicity and Maximum Recommended Dose, an article published in Environmental Health Perspectives, ca. August 2000: A review of the human trials on the safety of iodine ingestion indicates that neither the maximum recommended dietary dose (2mg/day) nor the maximum recommended duration of use(3 weeks) has a firm basis. Rather than a clear threshold response level or a linear and temporal dose-response relationship between iodine intake and thyroid function, there appears to be marked individual sensitivity...
    – chb
    Jun 30, 2016 at 23:04

Well it's been banned for sale in Europe for use in purifying water. (http://www.grough.co.uk/magazine/2009/08/13/eu-ban-will-end-walkers-use-of-iodine) As that webpage mentions Chlorine is an alternative, but leaves a nasty taste (although I believe you can add another chemical to neutralise the taste)

Alternatives are a water filter, or UV light serialisation.

  • 1
    It appears to be banned in Europe, not because it's dangerous under normal dosage, but because it's not proven 100% safe under any dosage. Feb 1, 2012 at 20:48
  • 4
    Chlorine is also a little harmful... General bactericides kill cells. A ban by Europe or California can be encouraged by politics or lobbying as easily as by science. Feb 1, 2012 at 22:32
  • 1
    Banned in Europe, eh? That's hilarious. Yep, chlorine is quite toxic. So is Vitamin A, but in small amounts it's a good thing. I switched to a Sawyer Filter for 2012, and I'm VERY happy with it. I still carry iodine as a backup in case something goes wrong with the filter. Dec 16, 2012 at 2:42

Pretty much all water tablets I've seen have been chlorine based here in the UK - I've used them on a number of occasions. In normal doses they don't affect the taste that much, and they have the advantage for people who don't know what they're doing that if they really overdose on the tablets the water will taste too foul to drink anyway!

If you don't want to use tablets or affect the taste at all, then hold the water at a rolling boil, and if necessary use a ceramic filter to remove any nasty metals that may be present. It's more hassle than just using tablets but the way to go if you don't have them or don't want to use them!

  • Depending on what you're trying to kill, you want to boil for at least 10 minutes. A couple of minutes is likely to kill anything a tablet would kill, but once you're boiling it, may as well leave it long enough to kill all the nasties ;) Feb 1, 2012 at 20:55
  • @RussellSteen This is true, edited accordingly - though it depends on the location and how much fuel you're carrying. Big difference between a dirty river that people dump sewage in and water collected from a clear stream on Dartmoor!
    – berry120
    Feb 1, 2012 at 21:37
  • I posted this comment earlier: The boiling time is definitely NOT true. Water only needs to reach the boiling point to become safe. Don't waste your fuel by boiling it for more than a moment. This is as per the Wilderness Medicine Institute's principles, as seen in this article: nols.edu/wmi/articles/archive/stomach.shtml But I retract it due to some conflicting sources. I'll reserve judgement until I see scholarly articles. Sorry.
    – Greg.Ley
    Feb 17, 2012 at 18:46
  • @Greg.Ley -- The CDC recommends at least a minute. More if you're at altitude. "To the boiling point" is not considered sufficient by most health organizations. 10 minutes may be excessive. 10 minutes was based on a discussion I had with a health professional recently regarding specific diseases. Feb 17, 2012 at 21:05

I think a good attitude towards these tablets is "emergency use" (which is labeled on the side of the bottle, not visible in the Amazon image). No good backpacker doesn't have these, but I suggest a water pump as the planned primary method. Note: there are also iodine "neutralizer" tablets that are supposed to remove the bad taste (you drop them in after the 30 minutes is up and wait another 30 minutes). In my opinion they barely change the taste and are not worth it. Anyways, you can take a tour to water purification large scale.... .............

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