Ascites necessitating persistent drainage or paracentesis after drain removal has been found among early postoperative complications after combined hepatectomy and cyst fenestration (CHCF) for polycystic liver disease (PLD). It has been reportedly observed in 20% to 70% of cases and seemed to easily cause recurrent symptoms unless properly treated. We utilized distilled water lavage for treating localized fluid collection after combined hepatectomy and cyst fenestration for PLD. A 63-year-old female patient underwent CHCF for PLD, which caused severe abdominal fullness. Early postoperative course was uneventful until 10 days after surgery when the patient suffered sudden abdominal fullness and resultant severe anorexia because of right subphrenic massive localized monolocular fluid collection diagnosed by abdominal computed tomographyalthough total liver volume was reduced to less than half of that before surgery. Percutaneous drainage relieved symptoms immediately, but the drainage tube could not be removed because of massive outflow. Then we utilized distilled water lavage for treating this condition. After that, drain outflow dramatically reduced and the drainage tube was successfully removed. Total liver volume of the patient continued to reduce up to 1 year after surgery and retained less than one-third of preoperative total liver volume thereafter. Sustained reduction of total liver volume in the present case suggested a sclerosant effect of hypotonic cytocidal property of distilled water for cyst endothelium and/or retrieved effectiveness of fenestration. Hence, we consider this approach to be useful for patients with PLD receiving CHCF and thus present it here.