if the question is related to water content in hydrocarbon's and you have a temperature and a pressure then a isothermal flash would solve your problem, take care to use a suitable thermodynamic model
You can also go to the GPSA Engineering Data Book, Figure 20-3. It has temperature on the x-axis and water content on the y-axis with lines for pressures. If you know a water content and need a dew point, you enter on the y-axis, go over to the pressure and down to the dew point. If you have dew point, enter on the x-axis, go up to the pressure, and over to the water content.
