Several studies have shown that time domain reflectometry (TDR) can be used to measure water content and solute concentration during steady‐state experiments with constant soil water content. Few studies have been carried out to identify the relationship between bulk electrical conductivity (σ a ) and soil solution electrical conductivity (σ w ) to be used for transient conditions with varying water content. In this study, a single TDR probe was calibrated and found to accurately measure water content and σ a . The σ a measurements were fitted to σ w using several previously published models. The accuracy of the σ a and σ w measurements increased with σ a ; however, the error in the σ w estimation was a higher than 5.7 mS m −1 . The calibration was verified in a large sand column; σ a measurements were fitted to σ w measured in soil solution extracted with suction samplers. The calibration was also used in a transient solute transport experiment. If not accounted for, the temperature effects of the water content measurement introduce significant errors in the σ w estimations.