The subject of this paper is to present the results of the research that took place on the ground dam of the small water reservoir Bezedník III, which is located in the Litava river basin. It was the first object which was monitored using the method of electrical impedance spectrometry (measuring system with alternating current) applying the apparatus containing a Z-meter device. The method has been selected to identify the observed changes, which were related to variable loads earth dam of small water reservoir by water, in time and space. The regular monitoring of the object was carried out in the years from 2006 to 2012 because of suspicion about its instability due to water loading. The control monitoring of the object was carried out in the years 2016 and 2018. The objective was to document anomalies of the construction of the earth dam in the form of electrical impedance maps, the life of the measuring probes and, at the same time, the adaptability of the measuring apparatus with the set of Z-meter devices. The impedances have been measured periodically in various layers. The initial impedance reached values of 0 to 2200 Ω and during the longitudinal study the values have changed up to three times in comparison with the initial state. The various layers have been proved to behave differently from the others concerning the measured phenomena.