Sea water intrusion causes fresh water shortage on small islands, and desalination systems are needed to desalt the salinated water (brackish water) and produce fresh water. Unfortunately conventional desalination technologies can only work properly with stable external power inputs, which are usually not accessible in these rural areas. In this study we propose an integrated self-desalination stack that consists of alternate anion and cation ion exchange membranes and couples the technologies of reverse electrodialysis and electrodialysis. The salinity gradient energy between sea water and brackish water is harvested to demineralize another portion of brackish water directly in the same stack. The overall process is spontaneous and energy self-sufficient with minimum peripheral devices, and it is promising to provide fresh water supply especially for these rural residents on small islands.