> I go through liters of water a day with my two humidifiers just to try to raise humidity by around 20 percentage points. In a small urban apartment that isn't much bigger than some people's whole suburban kitchens.
No surprise, that's because your water gets vented away…
My brother had a broken ventilation for a whole northern England winter in a flat he rented (and the landlord was too busy fixing this shit up), he had massive humidity issues with fungi spores making him sick before he understood what the problem was, and he'd tell you how much discipline it takes in manually venting your house by opening the windows to keep things from molding!
> A damp sponge isn't going to do a thing, and I can't imagine where you would ever have gotten the idea that it would.
Hey you know what, just do the math by yourself, it's just one pV = nRT away ! But of course, this is assuming you're not removing all that water directly as it evaporates.
> Moisture is not the primary reason for ventilation, except above showers -- it's to prevent CO2 buildup along with other toxic gases like CO and VOC's.
Maybe have a look at your local building code and see how the ventilation requirements are made. I've refurbished a house by myself and I did just that, it turns out the regulations are built on water extraction, as CO2 won't realistically kill or harm you, CO only matters in kitchens if/where you have gas stove (and in my country, this is subject to additional ventilation requirements in the kitchen itself independent of the house's ventilation), and VOC are only a recent concern. That's also why there have been hygrometer to pilot ventilation for a while.