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Seawater desalination by reverse osmosis was studied as an alternative process for the production of fi'esh water to supply 20,000 m3/d of drinking and boiler feed water at the Badak natural gas liquefaction plant and community housing. Seawater resources will be taken offshore from the Bontang Sea near the plant site, The chemical and physical analysis of seawater will be made at several locations in the Bontang Sea, which contains around 33,000 ppm TDS without any special characteristics. The Hydranautic RO design will be used for pre-design of the RO system. Data input needed for simulation are characteristics of seawater, production of fresh water and the price of energy at the local site. Total water cost ranges from US$ 0.46-0.64 based on an energy price of US$ 0.038 kWh at Badak. By simulation, product water had TDS 452 and boiler water feed TDS 15. Total investment cost based on 20,000 m3/dproduct ranges from US$ 8-16 million, depending on local site conditions. The area needed for a seawater RO plant is around 2500m 2. This study describes an idea and an illustrationabout other fresh water resources before implementation of RO seawater desalination at Badak before the fresh water resources dry out. The pre-design gave satisfactory results in the prediction o f total water cost and total investment for the RO plant.