Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. WAter vapor or water vapour, also aqueous vapor, is the gas phase of water. WAter vapor is one state of the water cycle within the hydrosphere. WAter vapor can be produced from the evaporation or boiling of liquid water or from the sublimation of ice. UNder normal atmospheric conditions, water vapor is continuously generated by evaporation and removed by condensation. WAter vapor is a greenhouse gas along with carbon dioxide and methane.