The Punpun originates on the Chota Nagpur Plateau, at an elevation of 300 metres (980 ft).

The river mostly flows in a north-east direction and joins the Ganges at Fatuha, 25 kilometres (16 mi) downstream of Patna.

[2] The 200 kilometres (120 mi) long river is mostly rainfed and carries little water in the dry season.

[2] This river is mentioned in the Vayu and the Padma Puranas in connection with Gaya Mahatmya as the punah-punah (again and again) of which Pun-Pun is the colloquial form.

[citation needed] The Puranas interpret the word punah-punah in a spiritual sense that sins are removed again and again by offering oblations to forefathers in the river.