A diffuser for diffusing liquid into surrounding ambient air, comprising: a base member having an upper surface and a lower surface; a liquid reservoir mounted to the base member over the upper surface thereof, the liquid reservoir having surfaces defining a receptacle for holding a volume of liquid therein; an ultrasonic transducer mounted to the base member over the upper surface thereof, at least a surface of the ultrasonic transducer exposed to any volume of liquid held within the receptacle such that ultrasonic vibrations of the ultrasonic transducer generate atomized droplets of the liquid over the volume of liquid held within the reservoir; a spout including an opening at an upper end thereof and being sized and configured to rest upon the liquid reservoir at a lower end of the spout; a fan mounted to the base member and configured to force airflow from an exterior of the diffuser, into the base member, around the receptacle of the liquid reservoir, into a volume of space enclosed by the spout and the liquid reservoir overlying any volume of liquid held within the receptacle, and out through the opening at the upper end of the spout to ambient air external to the diffuser, the forced airflow carrying the atomized droplets of the liquid generated by the ultrasonic transducer to the exterior of the diffuser through the opening at the upper end of the spout; the diffuser characterized in that it further comprises: a cover including an opening at an upper end opposite a lower end thereof through which the forced airflow generated by the fan passes, the cover sized and configured to enclose the liquid reservoir and the spout; and a polymeric gasket including a vertically extending wall encircling an exterior sidewall of the liquid reservoir and a flange, the flange disposed on a portion of the upper surface of the base member extending laterally beyond the exterior sidewall of the liquid reservoir and extending between the portion of the upper surface of the base member and the lower end of the cover. a base member having an upper surface and a lower surface; a liquid reservoir mounted to the base member over the upper surface thereof, the liquid reservoir having surfaces defining a receptacle for holding a volume of liquid therein; an ultrasonic transducer mounted to the base member over the upper surface thereof, at least a surface of the ultrasonic transducer exposed to any volume of liquid held within the receptacle such that ultrasonic vibrations of the ultrasonic transducer generate atomized droplets of the liquid over the volume of liquid held within the reservoir; a spout including an opening at an upper end thereof and being sized and configured to rest upon the liquid reservoir at a lower end of the spout; a fan mounted to the base member and configured to force airflow from an exterior of the diffuser, into the base member, around the receptacle of the liquid reservoir, into a volume of space enclosed by the spout and the liquid reservoir overlying any volume of liquid held within the receptacle, and out through the opening at the upper end of the spout to ambient air external to the diffuser, the forced airflow carrying the atomized droplets of the liquid generated by the ultrasonic transducer to the exterior of the diffuser through the opening at the upper end of the spout; the diffuser characterized in that it further comprises: a cover including an opening at an upper end opposite a lower end thereof through which the forced airflow generated by the fan passes, the cover sized and configured to enclose the liquid reservoir and the spout; and a polymeric gasket including a vertically extending wall encircling an exterior sidewall of the liquid reservoir and a flange, the flange disposed on a portion of the upper surface of the base member extending laterally beyond the exterior sidewall of the liquid reservoir and extending between the portion of the upper surface of the base member and the lower end of the cover. a cover including an opening at an upper end opposite a lower end thereof through which the forced airflow generated by the fan passes, the cover sized and configured to enclose the liquid reservoir and the spout; and a polymeric gasket including a vertically extending wall encircling an exterior sidewall of the liquid reservoir and a flange, the flange disposed on a portion of the upper surface of the base member extending laterally beyond the exterior sidewall of the liquid reservoir and extending between the portion of the upper surface of the base member and the lower end of the cover.