In time-lapse controlled-source electromagnetics, it is crucial that the source and the receivers are positioned at exactly the same location at all times of measurement. We use interferometry by multidimensional deconvolution (MDD) to overcome problems in repeatability of the source location. Interferometry by MDD redatums the source to a receiver location and replaces the medium above the receivers with a homogeneous half-space. In this way, changes in the source position and changes of the conductivity in the water-layer become irrelevant. The only remaining critical parameter to ensure a good repeatability of a controlled-source electro-magnetic measurement is the receiver position.