In a process for thermally degassing the water in a steam system, in particular a heat recovery steam generator, which steam system preferably includes at least one steam drum, at least one economizer connected upstream of it, and at least one evaporator, economic, efficient and structurally simple degassing is achieved by virtue of the fact that water is sucked out of at least one water volume, this water is mixed with steam from a steam volume, and the two-phase mixture that is formed flows out into the water volume.