I fail to see why you couldn't boil water in a nalgene container. I wouldn't put it over a fire, but wouldn't have a problem dropping hot rocks into a container full of water until it was boiling.

I mean, if you can boil water in a canvas hat, it isn't going to kill a nalgene container. There is no evidence whatsoever that "toxins" will be released in this process.

That said, I carry stainless steel cups on the bottoms of my nalgene bottles, so I don't have to heat rocks.

Greg