White Cap Mountain lies within the watershed of the Pleasant River, a tributary of the Piscataquis River, which drains into the Penobscot River, and into Penobscot Bay. The east side of White Cap drains into B Inlet Brook, then into B Pond, Guernsey Brook, and the East Branch of the Pleasant River. The north and northwest sides of White Cap drain into the West Branch Ponds, then into the West Branch of the Pleasant River. The south side of White Cap drains into Greenwood Brook, then into the West Branch of the Pleasant.