AquaMira liquid (two-part mix and treat) is the most cost-effective ClO2 option. The ClO2 tablets sold by AquaMira, Katadyn and others should be similarly effective, but when I pencil out the cost over time, they add up pretty quickly versus the liquid. Still, I always have a few in my emergency kit since they're simple to use and have long shelf life (despite what the package may say).

ClO2 is very effective against bacteria and viruses, but like all chemical treatment, is slow in treating cysts like giardia and crypto (half hour and four hour treatment times, respectively)

If you suspect giardia or crypto in your water source--from human or animal waste, especially grazing cattle--then filtration and/or UV is a faster, more reliable path. Bacteria, such as e.coli are well treated by ClO2. Prefiltering is always a good practice, since bacteria cling to particles (not to mention getting out the tiny swimmy things we often see in our source water).

I don't think Lori's statement can be overemphasized: good sanitary practices and reliable water treatment and storage are worth the bother and expense. This is one area I'm resolutely "mainstream."

Cheers,