In recent decades, the Electrical Resistivity Tomography (ERT) monitoring technique has introduced its capability to monitor the hydrogeological risks [1, 2]. The ERT method is especially efficient in monitoring the water content changes in the subsurface material. In this paper we present the results obtained from about two years of data analysis for the ERT monitoring data measured on a critical slope. A customized ERT monitoring system was installed in the study site in March 2022 and it is still in operation making at least two measurements per day. The resistivity meter supports a total of 48 electrodes that were deployed inside a trench, attached to anti-rodent multicables. The Wenner electrode configuration was used for data acquisitions and in order to satisfy the desired horizontal and depth data coverage, the unit electrode spacing 3m was selected. The main demand of the authorities was to define thresholds of attention for resistivity changes caused by the fluctuations of the water table, mainly after heavy rainfall events in the study site. Therefore, five piezometers were also installed along the ERT line to monitor the water table variations with time and these data were used to calibrate the relation between the resistivity values and the piezometric levels. In this paper we discuss the data analysis procedure to process seasonal ERT monitoring data and correlate the real resistivity values with the piezometric levels. Scatter plots were used to define the thresholds of attention based on the variation limits introduced by the geotechnical group of the end user.