To locate water bearing geological structures (fractures and layers), it is important to have a fair contrast in the electric conductivity between the water-bearing layers and fracture zones, and the adjacent formations. The resistivity of rock and soil is determined by the amount of mineral-conducting constituents and the content of more or less mineralized water in the pores' interstices. The latter condition is by far the most dominant factor. In fact, most rocks and soils are conductors for electric current due to internally contained water. The widely differing resistivity of the various types of impregnating water (meteoric water, sea water) alone can cause variations in the resistivity of rocks (sedimentary and igneous). This can range from a few tenths of an ohm*meter to hundreds of ohm*meters. This is the reason why the geoelectric resistivity method is the most useful geophysical method in groundwater prospecting.
There are two fundamentally different techniques of carrying out resistivity investigations: the resistivity profiling method and the vertical electrical sounding method (VES).
