The Glenderaterra Beck lies to the west of Mungrisdale Common and its tributary, Roughten Gill, forms the southern boundary. A further feeder on this flank is Sinen Gill, whose waterfall is one of the fell's most notable features. The River Caldew lies to the north, across which is Great Calva, most southerly of the Back o'Skiddaw fells. Despite its uninspiring appearance Mungrisdale Common does therefore stand on the important Eden-Derwent watershed, though it is not well defined at this point. Water from the southern flanks reach the sea at Workington while rain falling on the northern side heads for the Solway Firth via Carlisle. The watershed continues across Skiddaw Forest between the headwaters of the Caldew and Glenderaterra, linking onward to Lonscale Fell in the Skiddaw range.