You can drink a small amount of water when you have your blood drawn for a physical examination. Physical examination blood draw for dietary requirements are relatively high, generally not recommended to eat after the blood draw, more advocate fasting for examination, because fasting can make the digestive tract rest, especially some digestive juices are no longer secreted, on the body’s normal blood indicators will be more accurate, can provide doctors with better clinical information to facilitate the diagnosis and examination and treatment. As a physical examination, it is best to rest and not eat, as well as not drink water. However, some diseases, such as diabetes patients will always have the symptom of thirst, you can drink a small amount of water to moisturize the mouth without dryness. For some patients with high blood pressure and heart disease, you can take a small amount of water in the morning to deliver the oral medication into the body, so as to prevent high blood pressure during blood sampling, as well as cardiac accidents and so on.