Getting up in the morning with water in the mouth may be caused by improper sleeping posture, or it may be the cause of mouth ulcers. 1. Improper sleeping posture: sleeping close to one side or lying on your back while sleeping may compress your cheeks, resulting in saliva that cannot be swallowed and the phenomenon of water in the mouth in the morning. 2. Oral ulcers: an ulcerative injury that occurs in the oral mucous membrane area, there may be round or oval ulcer spots in the oral mucous membrane area, and there will be obvious pain, when oral ulcers occur, localized pain or stimulation of secretion of saliva, resulting in getting up in the morning with water in the mouth. Usually must do a good job of cleaning the oral area as well as hygiene, to avoid the emergence of oral diseases.