Study Region: We interrogate the water resources of the Upper Kaligandaki River Basin (UKGRB), in the remote Mustang District of northwestern Nepal. The Nepal Himalayas are a major reservoir of freshwater; yet the impediments to its exploitation by local inhabitants are manifold, including weak governance structures, steep and irregular terrain, and frequent natural hazards that are linked to climate change. The UKGRB is characterised by its extreme fragility, paucity of water and water-related data, and enormous variability of the effects of climate change on glaciers through time and space. Study Focus: The purpose of this paper is to elucidate catchment hydrology and local flow variability, before demonstrating the ways in which sustainable water resource management (WRM)can be achieved regionally. New Hydrological Insights for the Region: We present the local crop water balance, and suggest methods to reduce crop water requirements and to ensure a more equitable distribution of available seasonal flow. We also propose a series of long-term changes that are needed to secure sustainability. Then, we suggest that the principles of citizen science can help to improve the spatial coverage of data, generating new hydrological time series (e.g. river discharge), which can aid local decision makers in the WRM realm (e.g. irrigation scheduling). This approach has the potential to be scaled-up across the entire UKGRB (and, indeed, Nepal as a whole).