Patients undergoing a painless colonoscopy need to refrain from drinking water for 4 to 6 hours prior to the test. Because painless colonoscopy process needs to give patients anesthesia drugs, currently commonly used is intravenous anesthesia drugs, making the patient general anesthesia. If the patient drinks water, it may cause the water in the stomach to be unable to empty, and during the anesthesia process of the doctor, the patient is likely to vomit, which may cause aspiration, or even lead to asphyxiation, which may cause serious adverse consequences to the patient, so it is necessary to prohibit water for 4~6 hours before the examination. In addition to water fasting, patients also need to fast for 8 hours before the colonoscopy. If there is no endoscopic biopsy and treatment, painless enteroscopy can drink and eat after the patient is awake and has no abdominal discomfort. Patients should not make their own judgment to avoid adverse consequences.