In the papers of G.E. Archie and V.N. Dakhnov were presented formulas of dependence between resistivity (or conductivity) of soil and that of porous water. Such dependence shows that we need to know water resistivity, that means its study at each fieldwork area. In some areas places for groundwater are absent or restricted (boreholes, wells, springs) as places of surface water (rivers, streams, ponds, lakes). Can we measure water resistivity in pools? Immediately after rain such water has no relation with soil resistivity. The purpose of our study consists in determination the rules of ionic exchange between soil and rain water in time. In the paper [Brunet et al., 2010] the authors demonstrated results of water resistivity measurements at contact with soil in time. We wanted to check results of that experiment.