Quick Answer
Iodine tablets are not effective against certain microorganisms, such as viruses and some bacteria, and their effectiveness can be limited by factors like concentration and contact time. They also have a limited shelf life and may not be suitable for pregnant women or people with thyroid issues. Additionally, iodine can have unpleasant taste and odor effects.
Ineffective Against Certain Microorganisms
Iodine tablets are primarily effective against bacteria like E. coli, Salmonella, and Shigella, and against certain parasites like Giardia and Cryptosporidium. However, they are not effective against viruses like norovirus, rotavirus, and adenovirus, which can cause waterborne illnesses. In fact, a study found that iodine tablets were only 20% effective against norovirus.
Limited Shelf Life and Concentration Requirements
Iodine tablets have a shelf life of around 2-3 years, and their effectiveness can be compromised if they are not stored properly. Additionally, the concentration of iodine required to kill microorganisms can be quite high, typically around 5-6 milligrams per liter (mg/L) for 30 minutes. This can be challenging to achieve, especially in emergency situations where water purification equipment is limited.
Other Considerations
Iodine can also have unpleasant taste and odor effects, which can make it difficult to consume purified water. Furthermore, iodine can interfere with thyroid function, and pregnant women should exercise caution when using iodine tablets. In some cases, alternative water purification methods, such as boiling or filtering, may be more effective and safer.
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