Hydrological and glaciological data were gathered in the watershed (1.37 km2) of the Antizana Glacier 15 (0.7 km2) in the periods 1997–2002 and 1995–2005, respectively. In addition, tracer experiments were carried out to analyse the flow through permeable morainic deposits located between the glacier snout and the runoff gauging station. Over 11 years, the mean specific net balance of the glacier was negative (–627 mm w.e.), despite the occurrence of positive values in the La Niña years (1999–2000). From the glacier net mass balance between 1997 and 2002, it was found that the mean flow originating from ice melt was significantly higher than the mean discharge measured at the hydrological station. Analyses of tracer experiments and of the different components of the hydrological balance suggest groundwater flow that originates below the glacier accounts for the remaining water. This result is important for regional analyses of available water resources and for the relationship between hydro-cryospheric processes and volcanic activity.