Thanks to recent technological developments, apparent soil electrical conductivity (ECa) can now be mapped over large areas which provides new data for precision agriculture. However, in Mediterranean vineyards rooting depth can be greater than usual crop and the volume of the soil cover that needs to be explored is more important. This study examined the ability of an ECa map from mobile EM38 to predict water related vineyard variability on two fields. To depict ECa -vineyard relations, Electrical Resistivity Tomography (ERT) profiles and soil observations, (42 boreholes 4 meters deep) were made over 7 representative transects of both fields. In one of the fields, ECa map and NDVI map were found correlated whereas only weak correlations were found for the other one. The examination of ERT measures and soil observations in the former field showed a clear relation between soil electrical properties and soil properties known as influencing vine water supply (e.g. bedrock depth) and a good discrimination of ERT measures at the measurement depth explored by EM38. Conversely the later field showed that the ERT measurements are lower and not directly in relation with any of the soil differentiations that may causes variations in plant water. The contrasted performances between the two fields demonstrates the importance of a prior knowledge of soil patterns as a prerequisite to ECa survey