Usually always drink water or dry mouth may be physiological dehydration, diabetes, uremia and dry syndrome. 1. Physiological water shortage causes. The patient is in a hot environment, will lead to water shortage, part of the population will lead to drink water still dry mouth, dry tongue, but when the body’s water needs to meet the dry mouth and tongue discomfort will be relieved. 2. Diabetes. Diabetic patients due to high blood sugar in the body, will lead to tubular reabsorption of primary urine less, generally lead to polyuria, followed by dry mouth and tongue. 3. Uremia. Due to different degrees of antidiuretic hormone deficiency, or due to a variety of pathologies caused by renal insensitivity to antidiuretic hormone, resulting in the body polyuria, and then appear dry mouth performance. 4. Dryness syndrome. This disease is a chronic inflammatory autoimmune disease involving exocrine glands. Clinical generally manifested as dry eyes and dry mouth, causing patients with dry mouth, patients generally need to drink a lot of water, dry mouth is generally not obvious relief. Drinking water all the time or dry mouth, it is recommended to go to the hospital for further consultation.