first recovered drops. These values were very high in the beginning of the operating time, due to the high concentration of soluble salts (the starting point of salts leaching that exist in sand and activated carbon). It should also be noticed that these conductivity values were linked to the initial salinity of the sand. From 3 to 14 days, a stable value of the conductivity (3.5 mS/cm) with small changes between filters has been obtained. However, from 14 to 42 days, a decrease of the conductivity has been registered (1.2 mS/cm); the conductivity values of the seven filters being decreased. This refers to the height of activated carbon in each filter. This might be expected if taking into account the salinity parameter