In the woods, I use multiple water-purification products, from tablets to pumps. Product weight, speed of purification, and filtration type are criteria I assess to choose the right weapon against the bacteria, viruses and protozoa that may exist in a particular place.
Drop-and-dissolve tablets, including Potable Aqua iodine ($7, www.potableaqua.com ) and Katadyn’s chlorine-dioxide Micropur product ($12.95, www.katadyn.com), are my most common defense. They are relatively inexpensive, light weight, and easy to use just add a tablet into your water and let it fade away and do its stuff.
But tablets have a few limitations. You often have to wait 30 minutes or so for the chemicals to take effect. There is an aftertaste, too, especially with iodine. And for cryptosporidium, a nasty contaminant found in some areas, tablets will take four hours or more to neutralize, making them nearly unusable except for overnight application. …
Stephen Regenold updates the options in 2011: