In High Mountain Asia (HMA), ongoing glacier retreat affects human and ecological systems through reduced water availability. Rock glaciers are climatically more resilient than glaciers and likely contain potentially valuable water volume equivalents (WVEQ). In HMA knowledge of rock glaciers is extremely sparse and here we present the first systematic assessment of rock glaciers for the Himalaya, which encompass ~25,000 landforms with an estimated areal coverage of 3,747 km². We estimate the WVEQ of Himalayan rock glaciers to be 51.80 ± 10.36 km³ (41–62 trillion litres). Their comparative importance vs glaciers (rock glacier: glacier WVEQ ratio) in the Himalaya was 1:24, ranging between 1:42 and 1:17 in the East and Central Himalaya, respectfully. We show that Himalayan rock glaciers constitute hydro-logically valuable long-term water stores. In the context of ongoing glacier recession and mass loss, their relative hydrological value in mountain regions will likely increase and deserves greater study.