Always feel thirsty may be physiological thirst, blood volume insufficiency, diabetes, dry syndrome and many other reasons. 1. Physiological thirst: daily need to drink about two thousand milliliters of water a day, if you drink too little water, there may be physiological thirst, timely replenishment of water can be relieved. 2. Insufficient blood volume: the body needs a certain amount of water to maintain normal functioning, if you drink less water, you will be in a state of insufficient blood volume. When the blood volume is insufficient, the secretion of saliva will also be reduced, and the mouth is in a dry state, you will often feel thirsty. 3. Diabetes: most diabetic patients will have the symptom of thirst, it is recommended that patients go to the hospital as soon as possible to do a blood glucose monitoring. 4. Dry syndrome: Dry syndrome is an autoimmune disease, patients usually have dry eyes, dry mouth, enlarged salivary glands, parotid and submandibular gland lesions and other symptoms. If the patient usually drink enough water, but also often appear the symptoms of thirst, it is recommended to go to the hospital in time to do further examination, to clarify the cause of the disease and then timely treatment.