Doing colonoscopy bowel cleansing pulling out clear water is not almost impossible. Bowel preparation is needed before doing colonoscopy, but it is not necessary for the patient to pull out water, in principle, as long as there is no obvious fecal residue in the feces, if pulling out water can indicate that the intestinal cleansing is more thorough and clean, so doing colonoscopy to clear the bowel to pull out water is possible. In addition, the main purpose of bowel cleansing is to avoid fecal matter leading to unclear vision, thus affecting the results of colonoscopy. At present, the common clinical bowel preparation drugs are mannitol, compound polyethylene glycol electrolyte bulk, etc. It is recommended that before the examination should follow the doctor’s instructions to standardize the preparation can be, do not be too nervous.