Mixing laws have been used in hydrogeology for decades. In glacial hydrology, they are used to determine the contributions of the different reservoirs supplying the proglacial stream. However, some assumptions about discharge–solute matter and discharge–electrical conductivity (EC) relationships have led to erroneous conclusions. Analysis of a theoretical example indicated a hyperbolic relationship between discharge and solute matter concentration/EC for two reservoirs. We applied this approach to experimental data from the Baounet Glacier (Savoie, France), assuming that the proglacial stream is provided by a combination of watershed groundwater flow (diurnally stable and with high EC) and quick drainage from the glacier (low EC and discharge that change very quickly). Applying mixing laws allowed us to characterise these two flows and to separate the quick flows (glacial ablation and rainfalls). Copyright © 2011 John Wiley & Sons, Ltd.