Anyway, in answer to your questions: Organic chemicals, which contain carbon, are a known hazard to humans. There are thousands of them, so generalizing is difficult. But in general, boiling water contaminated with volatile organic chemicals (VOCs) will cause most of the chemicals to "cook off." Of course, that means it just goes into the air, so don't stand over the pot inhaling the fumes. Chlorine dioxide is primarily a germ killer that will eliminate bacteria and viruses, although it will also neutralize some phenols, a particular kind of organic chemical that's another potential health hazard.
As for iodine, it's an effective germ- and virus-killer. In the quantities used to kill bugs in water, the risk it poses to humans is about as close to zero as you can get. There is documentation about attempted suicides using iodine, which basically concludes that it's very difficult to check out that way. But you can certainly filter iodine-treated water. A filter with a carbon element, such as the MSR WaterWorks EX ($140; www.msrcorp.com) will eliminate any iodine taste. The carbon also helps eliminate or neutralize many organic chemicals.
As for ViralStop ($7.95 for a two-ounce bottle), it kills both viruses and bacteria. The maker, SweetWater, recommends using it with filtered water as a last-ditch defense against waterborne parasites. The filter gets most of the bacteria, or at least about 99 percent of them, while the ViralStopa chlorine-based purifiertakes care of the remainder, as well as any viruses, typically too small to be filtered.
So my advice: Use a filter with a carbon element, then go with the ViralStop. That's the easiest way to avoid any possible nasties you might confront in a water supply. Alternatively, just boil. That'll kill bacteria and viruses, and help remove many organic chemicals.
Meanwhile, keep an eye peeled for lightning, meteor strikes, and rattlesnakesB.