Potable Aqua Chlorine Dioxide Water Purification Tablets

This is the ultimate in light gear. The fact that you have to wait 4 hours to kill cryptosporidium is a little bit of a pain in that I always have to be sure to have enough drinkable water handy. This means I usually carry more than some others (during hot weather I'll carry 4 liters).  

I have thought of getting a pump but since I now only go backpacking with a group someone always has one anyway if I really got stuck. There is a slight smell (very slight, some people don't even smell it) but I don't detect any taste. 

It's a good lightweight purifier that kills pretty much everything.