With no clue, after reading this thread, I'd think I'd get sick as hell from drinking any water from any source, and that's just not true.

We all want to be safe, and err on the side of caution while backpacking, but you have to consider all things, so here are some things to consider about water, here in the U.S.

First off, viruses are pretty rare in water, and most waterborne bacteria are not harmful, in fact, some are no doubt good for you.

Standing water with algae in it is far more likely to contain harmful bacteria in harmful amounts than clear running water. Watersheds that have cattle grazing within them are much more likely to contain bacteria. Good, clear, spring water isn't likely to contain any bacteria or virus.

You're more likely to get sick from bacteria in water if you don't live near the source. You do build up immunities to bacteria common to local sources.

While backpacking, I'd have to suspect that personal hygiene is the biggest culprit when one gets sick, not the water. Wash your hands with soap after going to the bathroom, or use hand sanitizer (a dab of your alcohol fuel works for that), and you've greatly reduced your risks. I have never got sick from drinking water, or swimming in rivers or lakes or creeks, and I've swam in creeks with cows standing in them upstream from me all day. Now, I didn't drink the water by the glassfuls, but I certainly swallowed some.

I also have to suspect that using chlorine would kill the good bugs that are in your gut, making you more susceptible to bad bugs in the water. I'm not sure about iodine, but I do know that too much of that is not good for you either. I'll offer that for your long term health you want to avoid both of these treatments, and use them only when you have no other method of treatment and have reason to suspect the water source is contaminated. I'd rather filter and boil water than treat it with iodine or chlorine.

With good reason I suspect that taking antibiotics will increase your risks, so if you've used antibiotics recently you should probably err further on the side of caution, but again, in that case I'd boil and filter my water, not chemically treat it, that would be among the worst things I can imagine doing after taking antibiotics. You kill all the bugs in your gut and you could certainly die from an infection in short time. In fact, one of the only effective treatments for that very condition, which is often caused by taking too many antibiotics, is to ingest a small amount of human feces (from someone healthy) in order to replace all the good bacteria you killed with antibiotics. It's like the ultimate probiotic. ( I know you want a source for that. )

Here's an article that has some good common sense info to help qualify most the rest of what I said here. The main take away from that interview, for me, is to know your source.

In any case, I still strongly recommend chemical treatments as a last resort only.

Finally, the $19.99 "Lifestraw" filter I pointed to has some very impressive specs, especially considering the price and weight (2.0 oz). It's not likely you'll need anything more than it unless you're drinking hospital sewage from a ditch.

The company that makes it also makes a gravity filter that does remove 99.9% of viruses too, and it will be for sale in the U.S. soon. From what I can see, the Lifestraw Family Water filter-purifier is a very good option for backpackers. I'll sell you my katadyne hiker right now for $25 and wait for it.