With some on this thread recommending Polar Pure, it's time for my periodic account of "adventures with iodine."

About 5-6 weeks after I started using iodine to purify my water (only on weekends), I started to develop a rash. Not a surface rash--these were deep lesions (lichen planus) that itched horribly, took months to heal and left permanent scars. Since then I have not been able to eat seafood, anything with iodized salt (I have to avoid eating out and refuse invitations to peoples' homes) or multivitamin/mineral supplements (nearly all of which contain iodine). My latest outbreak was due to taking glucosamine/chondroitin (at my doctor's suggestion), which is derived from shellfish. Most of my food shopping time is spent reading labels--even the traces of iodine in sea salt are enough to cause an outbreak.

My dermatologist told me that allergies to iodine are not at all uncommon. And even for those not allergic, long-term use of iodine can cause thyroid problems. There's a reason the CDC says that iodine is for emergency use only. It is contraindicated for pregnant women and children, which should tell you something. And, as DTape says, it's not very effective against the primary nasties you're trying to eradicate. Especially in cold water (such as found in the Cascades and Rockies), it takes at least 4 hours to work. Several sites I've checked claim it's ineffective against protozoan spores (giardia and friends).

As a result of this experience, I refuse to use any chemicals in my water. I do take some Katadyn Micropur tabs along for emergencies, but I rely on my filter. My current one is the ULA Amigo Pro gravity filter, which takes a little longer but frees me from the back spasms I got while bent over the water source pumping. And it weighs less than most pump filters. I have my eye on the Steripen, though.

Even careful selection of sources doesn't mean you won't get sick. If people have been camping close to a spring, there are probably nasties in the wanter!