# How does volume of water in closed system relate to humidity at 25(C) degrees

If I have a closed system with a volume of 100L, at ~24(C) or ~75(F) degrees, what volume must be filled with water to reach a humidity of 90%?

I imagined if you fill it 100% with water, humidity is 100%? But I also imagine that with anything less than 100% filled with water, temperature becomes a limiting factor, and 90% humidity might not be achievable without raising the temperature.

I checked out a max humidity ratio table to see that at 25(C) the saturation pressure is 3130 pa, with a maximum humidity ratio of 0.019826 -kg(w)/kg(a) and that humidity ratio can be expressed with the partial pressure of water vapor:

x = 0.62198 pw / (pa - pw)

pw = partial pressure of water vapor in moist air (Pa, psi)

pa = atmospheric pressure of moist air (Pa, psi)

The maximum amount of water vapor in the air is achieved when pw = pws the saturation    pressure of water vapor at the actual temperature.


But this is as far as I got, as my understanding of humidity (relative, specific, etc).. is negligible... any suggestions or just a rough estimate?