I am no where near qualified to speculate on this entry, but I am going to try. If there is reduced pressure (to an extent), water vapor may stay water vapor. And if the whole equipment is on the same pressure, then you could have a desiccant tank with dried NaOH (or equivalent), before the mixer. Correct? As if you're processing the gases before the actual operation?
I'm sorry, but I am just starting my college career this Fall, but I have A-L-W-A-Y-S been into chemistry and have a rather immaculate setup here at my house to be doing such experiments. And maybe that's what you need to do. An experiment. Do you have a place and the proper equipment?
-Cobra