Abstract: A device for humidifying air with water vapor is provided, in which water is brought to boil by means of electrical current and evaporates. Minerals or dry residue contained in the water (4), in particular, lime, become separated, and fresh water containing minerals and dry residue is also refilled approximately according to the amount of evaporated water. The minerals or dry residue, in particular, lime, are removed from the container (2) that holds the water (4) to be evaporated immediately after its formation or during the evaporation. For this purpose, the water from the container (2) is circulated in a closed external circuit, for example, with a small pump (9). The circuit has a line (6), the filter (7), and a return line (8), as well as a mixing container (11), in which the fresh water enters via a line (12), so that it is led together with the cleaned water via a common line (13) back into the container (2).