All right, I'm not a doctor, but I didn't sleep through all of my biology classes in college. Our breath contains more water vapor than the surrounding air, unless you're in a steam room. Since engineers are concerned with keeping people comfortable indoors, they need to know this stuff and I found the following information on a site talking about the problems of handling the water vapor given off by large crowds in a closed building:
The average and comfortable humidity of air is around .5% water.
The human respiration contains around 6.2% water, at body temperature. We're talking steamy jungle type air. You'd need to be in a wet sauna to match this with the air around you. Without this extra water vapor going out, our throat and respiratory track would quickly dry out and cause all sorts of health problems. We wouldn't be able to talk, for instance.
But of course, the humidity of the miracle man's respiration wasn't checked, was it? The fact is, the human body is a big sponge, needing a fairly constant source of water to survive because of what we use up. We can go without food much longer than water, after all. We have a high rate of metabolism because of our size, mobility, and the energy requirements of a big brain.
