In this paper design and analysis of energy, exergy, economic and the environmental impacts (4E) of direct two-stage reverse osmosis (RO) system have been optimized for supplying Miarkelar water, north of Iran using multiobjective optimization. In this city, water has been provided for a period of 20 years and at the end of this period water is supplied for a population of 12,125 people. The calculation was based on the Caspian Sea water maximum TDS up to 13,000 ppm and permeate production of 4000 m(3)/day. The results present that optimal recovery and final price per cubic meter are respectively 76% and 0.37$. Feed water should be 10 degrees C preheated in power generation cycle condenser. Power needed for pumping is 362 kW. Based on these data, the organic fluids R290 and R717 have been selected for Organic Rankine Cycle (ORC), which have negligible environmental impacts than other fluids. Energy and exergy analysis was done according to this selection. Finally, considering the optimal design of a solar farm being matched with the HRSG with known Pinch and Approach temperatures, the results indicated that, R290 has the lowest desalinated water production cost compared with water and R717 and its cost is 0.568$ per cubic meter. (C) 2015 Elsevier B.V. All rights reserved.