In the depths of my bag resides one such tool, a small brown glass medicine bottle of the type that always seems to be unearthed when digging in the garden. It has travelled with me through the thirst-lands of the Kalahari, the frozen tundra of the artic circle, the scorched deserts of the Middle East and the teeming jungles of South East Asia . Its medicinal appearance is perhaps appropriate, as I depend on it to keep me healthy.

In the years that I have possessed this little 3oz bottle of unremarkable appearance, it has been used to treat almost 1000 litres of water, some of it decidedly foul. Yet the presence of a small pile of glinting metallic crystals trapped inside assures me that it will treat 1000 more.

Like some magical item from the rulebook of a dungeons and dragons game, from this deceptively small receptacle springs forth a seemingly unlimited supply of the means to create of one of the most fundamental requirements for life, safe drinking water

Thankfully ownership of such a miraculous item is not restricted to the socially challenged individual who has defeated the ‘High Elf Lord Malus Darkblade’ at a roll of the dice, as the inscription on the bottle hints at a more reality based existence: 

 “POLAR PURE WATER DISINFECTANT – Danger keep out of the reach of children”

Like all truly good tools, its brilliance lay in its simplicity.  It’s a stout brown glass bottle reminiscent of old fashioned medicine bottles but with a modern adult proof cap.

1. Examine that extremely clever dosage table, its printed in thermally sensitive ink like those T-shirts everyone used to have in the 80s. Because the required dosage is dependant on the ambient temperature, the heat sensitive dosage table automatically indicates how many capfuls of solution are required per litre of water to be treated, dispensing with the need for any brow furrowing mental arithmetic.

2. Once you have added the indicated number of capfuls to your water container, give it a shake and pour some of the water back into the polar pure bottle to replace the capfuls you took out, replace the cap and stuff it back in your bag.
   
   All those nasty bacteria, parasites and viruses will be dead in 10 to 20 minutes, and your water will be safe to drink. 1 bottle of polar pure will treat approximately 2000 litres of water before the crystals are used up, it is therefore easy to determine when its useful life is at an end, when the crystals are finally gone its all over. Having said that they last so long I normally misplace it or lose it to an officious customs officer long before I see the day those crystals vanish.

Unlike mechanical devices, the polar pure system has nothing to clog or jam and no moving parts to break or require maintenance. It has no batteries or filters which need replacing and requires no laborious pumping. There are no tablets that need crushing to be effective and it never goes off, it has an unlimited shelf life even after being opened and regardless of extremes of temperature, it simply keeps going and going and going, until the crystals dissolve away, giving you a clear indication of when it’s finished, no guesswork.

It’s much smaller and lighter than other systems with a comparable treatment volume; far more reliable than any mechanical device and at a cost of 0.008 of a penny for every litre treated it’s also the cheapest.

Its only drawbacks are those normally associated with iodine, you shouldn’t use it if you have thyroid problems or if you are pregnant, and then of course there is the taste. Like many people I don’t really notice the taste of iodine at concentrations of 3 parts per million, it’s certainly far less offensive than the taste of chlorine, but if the taste bothers you add a vitamin C tablet to your water after you’ve let the iodine do its work, and the Ascorbic acid will neutralise the iodine taste, its good for your immune system too!