15 Among the different contributions generating self-potential, the streaming potential is of 16 particular interest in hydrogeophysics and reservoir characterization for its sensitivity to water 17 flow. Estimating water fluxes in porous and fractured media using streaming potential data relies 18 on our capacity to understand, model, and upscale the electrokinetic coupling at the mineral-19 solution interface. Different approaches have been proposed to predict streaming potential 20 generation in porous media. One of these approaches is based on determining the excess charge 21 which is effectively dragged in the medium by water flow. In this chapter, we describe how to 22 model the streaming potential by considering this effective excess charge density, how it can be 23 defined, calculated and upscaled. We provide a short overview of the theoretical basis of this 24 approach and we describe different applications to both water saturated and partially saturated 25 soils and fractured media. 26 27