Water Treatment

Iodine
Iodine is an effective and economical means of purifying water, but note that iodine is not effective against cryptosporidium. Like pretty much all chemical purification systems, you have to wait for at least 30 minutes for iodine to take effect.

Iodine can be added into your water in two different forms, from pills or from crystals dissolved in water (see PolarPure). When exposed to any kind of moisture (even humidity in the air) iodine in a pill form can degrade quickly. PolarPure has inert iodine crystals that slowly dissolve in water so you don't get the instability that pills have (nor do you have to worry about pills breaking up completely in your water bottle before you drink it), but because PolarPure comes in a glass bottle, it can be broken. You also have the added downside of having to wait 30 minutes from the time you add water to the bottle of PolarPure and when it can be used to purify drinking water (if you plan ahead though, this isn't a big deal).

Iodine has a taste to it, so some people object to it purely on those grounds, although if you add a sugar mix to it (like gatorade or koolade) the sugar binds to the iodine and gets rid of the taste. Iodine should not be used if you have an allergic or hypersensitive response to it.

Hypochlorite
Hypochlorite is used by the company MIOX (it stands for mixed oxidants) to purify water. MSR and MIOX have come together to make the MSR MIOX. It takes a brine solution (from rock salt and water) and via an electric current it converts it to hypochlorite. The MSR MIOX inactivates viruses, bacteria, giardia, and even cryptosporidium (note, this is a purifier, and not a filter, because it is able to inactivate viruses). This purification system is issued to military personnel for good reason according to MIOX's site:

"Dugway Proving Ground, a U.S. Government laboratory, has been testing MIOX mixed-oxidant solution since the year 2000 on biological and chemical warfare agents. Findings show high efficacy against all agents, including Anthrax spores. Mixed oxidants achieved up to 99.99% inactivation of the spore, depending on the dose and contact time.

The mixed-oxidant solution also effectively destroyed the bacteria associated with Plague and the viruses associated with smallpox and polio. Mixed oxidants were also extremely effective against the nerve agents Soman (GD) and V-Agent (VX) and the blister agent Lewisite (L)."

Of course, this is assuming an adequate amount of contact time which can be a long time to wait. For example, the MSR MIOX is able to inactivate Hepatitus to an undetectable level, but it takes 60 minutes and cryptosporidium can be eliminated to a near undetectable level, but that takes as long as 240 minutes. Although this is a long time to wait, when you bear in mind that other systems, including filters, can't eliminate both cryptosporidium and water born viruses, you definitely begin to see the advantage of this system.

The mixed oxidant solution is colorless and tasteless, so it doesn't suffer the same disdain that iodine does. Although the MSR MIOX is waterproof and durable (it can take up to an eight story fall) it has not became the most favored system primarily because of its price tag of about $130.

Chlorine Dioxide
The chemical chlorine dioxide is extremely lightweight and although it's effective this approach takes approximately 35 minutes. The chemical taste is very mild. Chlorine Dioxide is effective against Cryptosporidium.