Suppose you have a gaseous mixture of nitrogen and pure steam (no liquid water), at temperature $T$ and net pressure $P$. The mole fraction of steam in the mixture is $x$. You are told that the steam is saturated.
I want to find temperature $T$ of this mixture.
I know I can find saturation temperature of water knowing saturation pressure of water. How do I know what is the saturation pressure? More specifically, is the saturation pressure of the steam equal to the partial pressure of the steam, $xP$, or the net pressure of the mixture, $P$?