Causes of anal fistula has a hard lump of running water, the reason is mainly rectal perianal abscess, intestinal tuberculosis and perineal surgery postoperative infection. 1. Rectal perianal abscess: after the formation of abscesses around the rectum or anal canal, these abscesses ulcerate on their own or are cut and drained, forming an external opening in the perianal skin, that is, the formation of anal fistula. The skin around the fistula is stimulated by inflammatory factors and papillary protrusions or granulation tissue bulge, feel like a hard lump, and the fistula is often accompanied by continuous or intermittent flow of purulent secretion. 2. intestinal tuberculosis: patients with intestinal tuberculosis in the gastrointestinal pathogenic bacteria will increase, which can lead to increased levels of toxins carried in the stool. If the broken anus is repeatedly infected by this stool, it may cause a perianal infection, which can develop into an anal fistula with a continuous flow of pus from the fistula. When the tuberculosis encroaches into the fistula, a hard lump may be felt. 3. perineal surgery postoperative infection: if after the perineal surgery is not strictly disinfection sterilization, so that the local wound infection, may be involved in anal infection, the situation is serious can develop into anal fistula. The surrounding tissues are infiltrated by inflammatory cells for a long time and may swell and harden. And the fistula will flow out a lot of purulent secretion, like running water. If the anal fistula has a hard water, there may be other causes, it is recommended to go to the regular hospital in time to identify the cause, follow the doctor’s instructions to accept the standardized treatment of professional doctors, to avoid aggravation of the condition.