Istisu is a mineral water source in the Sharur-Daralayaz uezd of the former Iravan governorate, later in the former Pashali (Azizbeyov, Vayk) district, and currently in the Vayots Dzor province. It was marked on five-verst map of the Caucasus. At present, it is located in the area of the town of Jermuk.