We report the results of experiments conducted under the well known ACS ED membrane, using the membrane potential technique, in order to obtain the transference numbers of Na+ and Br- before and after lengthy filtration studies using brackish waters from France and Senegal. With a change of the Br- transference number from 0.97 to 0.22 during the operation, the membrane charge was reversed due to irreversible adsorption of water resource ions. The same observation occurred for the CMX ED membrane. Then we decided to develop an autopsy approach before chemical or electrochemical modifications in order to adapt the commercial membrane material better to very highly salty water resources.