Appendix B
Page 4
Weight: 2 oz.
Widely available through suppliers of outdoor products
Also sold as Globaline and EDWGT (emergency drinking water germicidal tablets)
Instructions
One tablet is added to one quart of water. In cloudy or cold water, add two tablets.
Contact time is only 10-15 minutes in clear, warm water, much more in cold, cloudy
water (refer to table X).
Potable Aqua is now sold with "neutralizing" tablets made of ascorbic acid. Ascorbic
acid converts iodine to iodide, removing the taste and color.
Comments
This method was developed by the military for troops in the field. Advantages are unit
dose and short contact time, but these concentrations create strong taste that are not
acceptable to many wilderness users. The military requirements dictated a short contact
time (10 minutes in clear, warm water); thus the relatively high concentration of iodine
(8-16 ppm). With adequate contact time, and moderate temperatures one tablet can be
added to 2 quarts of water to yield 4 ppm of free iodine (Table 15). Rather than use two
tablets in cloudy water, clarify the water first.
Ascorbic acid (vitamin C) neutralizer reduces iodine to iodide, which has no
color or taste, but also has no disinfecting action. Esthetically, iodine is "removed" from
the water. However, iodide is physiologically active, so concerns about toxicity or
physiologic activity remain. For short-term use, iodine is safe and removing the taste is a
major benefit.
