Chlorine dioxide is used in an increasing number of water treatment plants, and is rapidly becoming the favorite for camping, travel water treatment.
ClO2 is a gas, light sensitive, and extremely unstable--it can explode when compressed or exposed to light. This makes in nearly impossible to transport .
It is generated by adding two different stable powders to the water.
ClO2 is always generated just before use, usually as a solution.
The powders are available for drinking water treatment compressed in tablets in the correct proportions. Or in two separate containers to be mixed with water to kill biological contaminants. It kills everything: viruses to bacteria to larger plasmids like malaria and other parasites.It breaks down into calcium or potassium chlorate.
http://en.wikipedia.org/wiki/Chlorine_dioxide or google "ClO2"