Give geographical reason:
Air becomes saturated.
When the water evaporates from the earth, it is released into the air. The air has a maximum ability to hold moisture in a certain quantity and at a particular temperature only. When this ability is reached, and relative humidity reaches 100%, the air is considered to have reached its saturation point.
In other words, when the proportion of water vapour and the vapour holding capacity is equal, the air is said to be saturated.