Field estimation of the soil water flux has direct application for water resource management. Standard methods like tensiometry or time domain reflectometry are often difficult to use because of subsurface heterogeneity, whereas noninvasive tools such as electrical resistance tomography, nuclear magnetic resonance, or ground penetrating radar are limited to the estimation of the water content. We present an electrical method that provides water flux estimates: streaming potential (SP) monitoring. This cost-effective tool may help to estimate the nature of the flow process (infiltration or evaporation) in the vadose zone. We discuss interpretation strategies in terms of numerical modeling of both hydraulic and electric processes in the vadose zone and propose an inversion scheme that allows the soil hydraulic parameters to be estimated from in situ infiltration experiments.