We provide a thermoeconomic assessment of electrodialysis indicating that the technology is most productive and efficient for the partial desalination of feed streams at the higher end of the brackish range of salinities. After optimising the current density to minimise the sum of energy and equipment costs, we demonstrate that at low feed salinities the productivity, and hence equipment costs, of electrodialysis are hampered by the limiting current density. By contrast, at higher feed salinities both productivity and efficiency are hampered by the reduced chemical potential difference of salt in the diluate (low salinity) and concentrate (high salinity) streams. This analysis indicates the promise of further developing electrodialysis for the treatment of waters from oil, gas and coal-bed methane as well as flue-gas de-sulphurisation, where the partial desalination of streams at the high-end of the brackish range can be beneficial. (C) 2014 Elsevier B.V. All rights reserved.