The amount of water to be consumed before taking electrolyte preparations for a colonoscopy varies from person to person, and usually requires 2,000-4,000 ml. Before doing colonoscopy, bowel preparation is usually required, and the examinee needs to empty the bowel. One of the commonly used drugs for bowel preparation is compound polyethylene glycol electrolyte bulk preparation, which is divided into type I, type II, type III, and type IV, with certain differences in the method of configuration and method of administration. Take Compound Polyethylene Glycol Electrolyte Bulk Type III as an example, it is mainly used for adults, one bag of the preparation needs to be dissolved with 1000 ml of water, and the amount of drinking water needs to be based on the body weight, generally 15~20 kilograms need to be given 1,000 ml of water, and the average amount of drinking water, generally 3,000~4,000 ml of water. Taking compound polyethylene glycol electrolyte dispersant type II preparation as an example, each bag of specification I needs to be prepared with 1,000 ml of water, and specification II needs to be prepared with 2,000 ml of water, and the amount of water needed for one examination in an adult is about 2,000 to 4,000 ml of water. The goal of bowel preparation is to discharge fluid in the form of clear water or yellowish water without residue, and it is recommended that 1~2 days before the colonoscopy should be based on food with less residue as much as possible. Take medications as prescribed.