Polar Pure is an iodine treatment system consisting of a tiny jar containing a few grams of iodine crystals.
You basically fill up the jar with water, wait a half hour until the water is saturated with iodine and pour this liquid into a bottle containing the water you want to treat. Instructions on the bottle explain how much to add for a given quantity of water.
Because the water in the jar will only absorb so much iodine before it reaches saturation concentration, the crystals last for about 2000 litres and when you pour the mixture out the crystals are retained in the jar by a clever plastic neck so you can then refill the jar and reuse many times. Because iodine does not degrade over time so you can use the same bottle until the crystals are all used up.
I’ve been using the same bottle of Polar Pure since 1999 and still have another decade of treatment left. I carry Polar Pure in my backpack whenever I’m travelling in a country without trustworthy water and sanitation just in case I’m caught without access to clean water.
You can purchase Polar Pure from my shop.