Scar Ridge stands within the watershed of the Pemigewasset River, which drains into the Merrimack River, and into the Gulf of Maine at Newburyport, Massachusetts. The northeast side of Scar Ridge drains into the Hancock Branch, a tributary of the East Branch of the Pemigewasset River. The southwest side of Scar Ridge drains into Telford Brook, Mack Brook, and Little East Pond Brook, all of which drain into Eastman Brook, and thence into the Pemigewasset.