Water vapor in the air
Liquid water can evaporate and turn into water vapor. Conversely, water vapor in the air can turn into the water again. The desert is arid without any moisture. On the other hand, public baths are very humid because they have a lot of water vapor. Thus, the amount of water vapor in the air is constantly changing.
The “saturation state” is the state in which air contains the maximum amount of water vapor. “Saturated vapor” is the maximum amount of water vapor that can enter the saturated air 1m3. As the temperature rises, the amount of saturation vapor increases. Therefore, warm air can contain more steam than cold air.
Relative humidity
The relative humidity is the ratio as a percentage(%) of the current water vapor to the saturated water vapor. A higher percentage means that the air–water mixture is more humid. At 100% relative humidity, the air is saturated and is at its dewpoint.
