The knowledge about the hydraulic conductivity of the subsurface is crucial to know as it is a main parameter for groundwater flow characterization within an aquifer. The geophysical method time-domain Induced Polarisation has been shown to be useful for estimating the hydraulic conductivity. By using a new inversion approach, where we directly invert for hydraulic properties as inversion parameters, the estimation of the hydraulic conductivity can be improved. We have measured at several test sites across five European countries, all characterized by unconsolidated sediments, but with differences in terms of the water electrical conductivity. In particular, at the Zeeland site in the Netherlands, a strong gradient in the water electrical conductivity is present since a freshwater lens is overlaying the sea water. A very good agreement between the hydraulic conductivity values from the inversion with the present …