Box 16-2 Disinfecting Drinking Water with Iodine

Some hikers use iodine to disinfect water from streams and lakes to make it safe to drink. Iodine is more effective than filter pumps, which remove bacteria but not viruses, because viruses are small enough to pass through the filter. Iodine kills everything in the water. A disadvantage of iodine is that it is a diuretic—increasing the frequency of urination. 

When I hike, I carry a 60-mL glass bottle of water containing a few large crystals of solid iodine and a Teflon-lined cap. The crystals keep the solution saturated with I2. I keep the bottle inside two layers of plastic bags to prevent I2 vapor from attacking everything in my backpack. 

I use the bottle cap to measure out liquid to add to a 1-L bottle of water from a stream or lake. The required volume of saturated aqueous I2 is shown in the table. For 

Vitamin C, a reducing agent present in many foods, reacts rapidly with I2  

Beverages such as the orange drink Tang are loaded with vitamin C. Don t put Tang or other beverages in the disinfected stream water until the 30-min waiting period is over. If you add the beverage too soon, it consumes the I2 before the water is disinfected. 

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