Most children of school age who wet the bed at night have what doctors term primary enuresis.. They have never had nighttime control of their bladder. Family history plays a role, too, in incontinence in children. If you wet the bed as a child, don't be surprised when your child does, too.
One thing to notice is that if you put a gallon of air on a scale, (in a wieghtless container, of course) you would measure zero, exactly. That's because the buoyancy caused by the surrounding air exactly counteracts the weight of the air in the container. If you pressurized the air in your gallon container to, say ten times the outside pressure (or 147.0 psi absolute, or 132.3 psi gauge) it would now weigh nine times 0.01, or 0.09 lb.
F and 50% relative humidity, there are approximately 107 grains of water per pound of humid air. A value of 107 grains in a pound of air is basically 107 / 7,000 grains per pound = 0.015 pounds of water in a pound of humid air. Sparing the details, that is a little over 8 grains of water per cubic foot of air.