Sublimation is the process by which solid water changes directly to vapour phase without passing through the intervening liquid phase. The gradual disappearance of flakes of ice during periods when the temperature remains well below freezing is an example of sublimation.

Evaporation is the process by which liquid water changes into vapour at ambient temperature. Water evaporates from all aquatic bodies as well as from wet surfaces. Evaporation from the ocean surface is by far the largest source of atmospheric water vapour.

Transpiration refers to the loss of water'in vapour form from plant leaves. On land, transpiration is considerable. For example, the loss of water through transpiration alone by one hectare (2.5 acres) of corn approximately amounts to 35,000 litres (8800 gallons) of water each day. Water loss from'a vegetatedmea takes place both by evaporation and transpiration and it is referred to as 'evapotranspiration'.