WHAT YOU SHOULD KNOW ABOUT IODINE FOR WATER PURIFICATION

Important: Water that has been disinfected with iodine is NOT recommended for pregnant women, people with thyroid problems, those with known hypersensitivity (allergic) to iodine. Not recommended for continuous use for more than a few weeks at a time.

When planning a long backpacking trek in the deep woods or an emergency preparedness kit, water treatment is surely at the top of your list. After all, you couldn't possibly pack and carry, or store enough potable water to last a week or longer.

Iodine tablets and drops are a very popular choice for various reasons:

kills most viruses and bacteria with little effort
more effective and quicker than chlorine
less expensive.
easy to pack and carry
easy to use

However, there may be a few things you don't know about iodine for water treatment.

Iodine, like chlorine and bromine, is a "halogen" - its Atomic number is 53 on the periodic element chart - All halogens are TOXIC.
Iodine, as all Halogens, is ineffective for treatment of water infected with parasitic worm eggs
Iodine is not effective against parasitic worm eggs and larvae.
Iodine is not effective against Cryptosporidium – a waterborne, disease spreading protozoan that contaminates drinking water supplies, causing intestinal infections in human beings and domestic animals.
Iodine has a low to moderate effect against Giardia lamblia - a protozoan parasite that colonizes and reproduces in the small intestine, causing diarrheal illness known as giardiasis.
Iodine tastes bad - some people counter the taste by adding vitamin C, but you must be sure to add the vitamin C after the iodine has had time to be effective, Vitamin C is a de-halogen and can actually neutralize the iodine's ability to purify your water
Iodine is not recommended for use by pregnant women or individuals with thyroid problems.
Iodine Allergy - Some people are allergic to iodine - if you're allergic to shell fish you probably shouldn't use this method of water purification. Symptoms of allergic reaction can vary from a runny nose and itchy, watery eyes to anaphylactic shock.
Iodine does not remove or neutralize agricultural and industrial chemicals, or heavy metals from water.
Iodine can react with certain contaminants causing residual chemicals or byproducts in drinking water after treatment is complete
Iodine effectiveness depends on the water temperature - iodine disperses slower in colder water
Iodine can lose effectiveness after a certain amount of time. Exposure to heat, humidity, moisture, and air will reduce the effectiveness of iodine tablets.