Abstract: A method and apparatus are disclosed for using ultrasonic energy in conjunction with an ultraviolet water sterilization system. An ultrasonic transducer assembly is placed in or around one end of the sterilization chamber for producing the ultrasonic energy. Ultrasonic vibrations are then applied automatically on a regular and intermittent basis to clean the components within the sterilization chamber and disrupt the chemical and physical action which causes scaling due to dissolved minerals and organic materials in the water. The ultrasonic vibrations cause a preventative cleaning action by the streaming and stirring of the water. Actual cleaning action is also created by cavitation and sweeping actions. The sweeping action is accomplished by frequency modulation which, by creating varying hot and cold spots within the sterilization chamber, allows for a uniform cleaning of a quartz sleeve encasing a UV lamp within the sterilization chamber. Ultrasonic vibrations also create a germicidal action.