A daily measurement of water conductivity has been recorded at the inputs and outputs of the column. The variation of conductivity as a function of time is shown in figure 2. Analysis of these values led to two significant observations. The filtered waters were characterized by an important conductivity exceeding 45 mS/cm for the first recovered drops, namely significantly above the values observed for wastewater (0.738 to 0.839 mS/cm) and raw water conductivity was usually stable within the interval of 7 to 77 days. The second observation concerned the conductivity curve which showed three parts. The first three days were characterized by a remarkable decrease of the conductivity values. It represented the leaching stage of filters [17]. During this step, high conductivity values were obtained, especially for the