A 34-year-old woman was admitted to our hospital in October 2022 because of night fever, dry cough, weight loss, and dyspnea of a month’s duration. Her chest CT showed diffuse ground glass opacification and small centrilobular nodules in both lung fields. Lymphocytes occupied a high proportion in the cells recovered from the bronchoalveolar lavage fluid, and Mycobacterium avium was also detected. Histopathological findings in transbronchial lung biopsy (TBLB) tissue showed from the invasion of inflammatory cells that lymphocytes were dominant, and non-caseating granuloma. Treatment with prednisolone decreased the symptoms, but they reappeared when the patient returned home after discharge from our hospital. M. avium was detected from bathtub water in the home. However, the symptoms only appeared when the micro-bubble function was used. Aspiration of aerosolized bathtub water contaminated with M. avium through the micro-bubble function caused the onset of this hypersensitivity pneumonitis