Drinking a lot of water or dry lips, may be a normal physiological phenomenon, may also be due to diabetes, hyperthyroidism, dry syndrome and so on. 1. Normal physiological phenomenon: the climate is dry in the fall and winter seasons, some patients will often drink water but the lips are still very dry, which is a normal physiological phenomenon. 2. Diabetes mellitus: Diabetes mellitus can lead to osmotic pressure increase because of the elevation of blood sugar, which is manifested in the situation of drinking water frequently but still dry mouth. 3. Hyperthyroidism: due to the abnormal function of the thyroid gland, it will lead to the body’s metabolic rate is higher than normal, and the patients can show that they often drink water but still have a dry mouth. 4. Dry syndrome: mostly related to the body’s autoimmunity, which can lead to a decrease in the secretion of glands throughout the body, often drink water, but still dry mouth. Drinking how much water or mouth has been dry symptoms continue not to ease or aggravate, should promptly consult a doctor, after a clear diagnosis, active treatment.