When using iodine drops I know that the procedure is to double the amount when the water is cloudy or cold and iodine is part of the make up of Potable-Aqua. However I can't say positively that this rule applies with the Potable-Aqua. Also Potable-Aqua does loose its potency over time. There for the tablet should be inspected at least annually. The tablets should be a steel gray color. After time they will turn an orange rusty color. A few tiny spots are acceptable.<br>During a survival course in Texas I used them to purify water from a muddy stagnant cow pond. I really have faith in them now! <br><br><br><br>