If the humidifier B 250/300/500 has a direct water connection, the external water monitor can be used as an additional safety device. In contrast to the safety water sensor, the water monitor has an independent solenoid valve that is connected between the safety pressure hose and the water tap The sensor of the water monitor is located in the safety drip tray and stops the water supply to the humidifier if it comes into contact with water. In addition, a signal tone sounds, which is only deactivated when the power supply is interrupted.