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Step 3: Add the Iodine Tincture

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Dip your eyedropper into the iodine tincture and squeeze up some of the liquid. Carefully position the eyedropper over the mouth of the bottle and add 5-10 drops per 32 fluid ounces (about 1 liter) of water. The exact number of drops is a personal choice (I can't make this decision for you) depending on the following factors:

The water source: if your source is a lake or some other still body of water, you want to add closer to 10 drops; if the source is flowing, you can add fewer.
The clarity of the water: you should add closer to 10 drops if the water is cloudy.
Your own aversion to the taste of iodine: some people hate the taste of iodine (it is a little bitter, and you will notice the taste in your purified water). If this is the case, you might want to add closer to 5 drops.

Personally, I'm a fan of 8 drops. If you are filling up a bottle or container that is not 32 fl. oz. or 1 liter, change your measurements accordingly. A 2 liter bottle will require twice the number of drops.