By adding a third chamber in between the two electrodes of a standard MFC and filling it with sea water, the cell’s positive and negative electrodes attract the positive and negative salt ions in the water and, using semi-permeable membranes, filters out the salt from the sea water, as seen in Fig. 5. Salt removal efficiencies of up to 90% have been recorded in laboratory work, but much higher removal efficiencies are required to produce drinking-quality water