In reply to Godwin:
> Do they really work, seem to good to be true. I actually have one, had it for years, but have never trusted it, when it actually came down to it.
I used one in Himachal Pradesh for a couple of weeks. Drank the mains water in the village, in which I dabbled the gadget. Followed the advice about food etc in the Asia thread. No problems whatsoever with food or drink.
As ebdon correctly says, you need to start with water that's reasonably clear and free from debris. If it's not clear the UV won't work properly.
Haven't used it since, as it's rare I'm in a situation where I not able to carry sufficient water for my needs, but I'd give it a go on possibly farmyard-infused streams etc.