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In the course of the transfer of precipitation into rivers, water is temporarily stored in reservoirs with different residence times^, such as soils, groundwater, snow and glaciers. In the central Himalaya, the water budget is thought to be primarily controlled by monsoon rainfall, snow and glacier melt^,, and secondarily by evapotranspiration. An additional contribution from deep groundwater^,, has been deduced from the chemistry of Himalayan rivers, but its importance in the annual water budget remains to be evaluated. Here we analyse records of daily precipitation and discharge within twelve catchments in Nepal over about 30 years. We observe annual hysteresis loops—that is, a time lag between precipitation and discharge—in both glaciated and unglaciated catchments and independent of the geological setting. We infer that water is stored temporarily in a reservoir with characteristic response time of about 45 days …