Does anyone's cars drink coolant?

I have the problem that when I run the A/C, I notice that after I turn the car, and the car cools down, that some coolant from the resouvoir disappeared. Looking at all the hoses, I can't detect any sort of leak anywhere. I am NOT running a A/C fan right now, but my car has yet to overheat (I only run the A/C when I'm on the highway, at a good speed).. I also haven't noticed any coolant coming from my exhaust. I notice that the resouvoir has condensation in it when the engine's real
hot, so is it possible that the coolant is escaping the resouvoir by steam?

Ideas?

 

A certain amount of coolant does evaporate. Approximately how much are you losing?

 

I would say in any given heat up/cool down, I will lose about
1/10th of a liter. But definitely in a week, all of the fluid would be
gone from the resouvoir.