2 cm 2 or less fig1 a to 13 f show an embodiment of an air humidifier with a water reservoir region thereby fig1 a shows a view from above fig1 b a perspective view of a lower region of the humidifier fig1 c and 13 d the respective regions of the humidifier sectioned along the planes c c and d d respectively in fig1 a fig1 e a view of the lower region of from above and fig1 f this region sectioned along the line f f in fig1 e in fig1 b one can see that the water reservoir region 71 is designed surrounding the water receiving region the passage 72 is formed by a small opening in the side wall 51 of the water receiving region only a single uv led light source 41 is necessary in the represented embodiment due to the limited size of the beaker like volume forming the water receiving region 5 this is arranged below the water level such that it is couples uvc light into the water reservoir region through a window 45 u2014 for example of quartz glass in fig1 c one can also see a circuit board 91 on which the uv led chip 41 is assembled and contacted as well as a cooling body 92 for cooling this chip 41 the housing of the humidifier is shaped such that the light source and the contactings etc of this are arranged on the side that is away from the water i e is the water free region is led laterally to the water receiving region at the location of the light source as one can see for example in fig1 an arrangement of the at least one light source on the lower side of the water.