Soil electrical conductivity (EC_a) by the four electrode method was studied in the laboratory as a function of soil water electrical conductivity (EC_w) and water content in six soil types. A linear relationship between EC_a and EC_w was valid only at salinities > 4 mmho/cm. At very low salinity levels the contribution of the surface conductance was not constant and had a higher contribution than EC_w to measured EC_a. A method for calculating the partial contribution of surface conductance to EC_a as a function of EC_w and clay content is applied including a correction for dependence on the soil water content.