We use these for our water purification system.
A single tablet will treat 1 liter of water, so we need two each time we fill our platypus.
We've experimented with tiny water filters, aqua mira and iodine tablets. These win for me hands down.
First, I don't have to squat for 45 minutes pumping a cubic inch at a time to get my water, nor do I have to mess around mixing chemicals, and finally there's no weird after taste like with iodine – so no need to carry gatorade powder to hide it.
The MicroPUR tabs are based on Chlorine Dioxide (which I believe is what municipal water treatment plants use for your home), and so can even treat giardia, but you have to leave them for 4hrs to do that. We usually let them run for 30 minutes which kills most things.
The first time I used them, we had a bag of really cold water collected, dropped the tabs in an they started smoking as they reacted with the water, releasing a strong chlorine odor. It was a little disconcerting, but after 30 minutes the odor and taste had gone completely.
This system works for us, because where we hike we are mostly guaranteed access to good water – streams, lakes or rivers. If I was planning a trip where I had to use murky or sketchy water, I'd bring my filter again.
Three sheets of them weighs in a less than 1 oz..
The obvious downside is cost. It is not the cheapest way to treat your water, but hey – the cost of going Ultralight? Priceless.
Available from Amazon for $12.95.