The Rhine-Weser watershed runs through the Dammersfeldkuppe. The source of the Schmalnau is on the northern flank of the mountain; its waters flow through the Fulda into the Weser. On the mountain's southern flank rises the Kleine Sinn (Little Sinn), the Bavarian name of the Schmale Sinn, whose water makes its way via the Sinn, Franconian Saale and Main to the Rhine.