The saturation point is the point at which air is unable to absorb more water. Saturation point can also be referred to as dew point. It can also be stated that a saturated liquid, such as water or a saturated vapour, contains the maximum amount of heat energy without boiling or condensing.

The h,x diagram shows humid air at 1013 mbar. It can be used to determine the absolute water content of the humid air (x), relative air humidity (%), temperature (oC) and enthalpy (h).