The salinity of the ground water in Berjand, the capital of the province of South Khoorasan in Iran, has been a matter of concern since the ground water is the only source of drinking water in the city. Firstly, the authors studied the effects of both nano-filtration (NF) and reverse osmosis (RO) for the reduction of total dissolved solids (TDS) in the north and the south of the city. Secondly, we applied the Reverse Osmosis System Analysis simulator to the pilot study under the same circumstances as the pilot study to investigate the suitability of the software as a predictor of water quality. The results of the pilot study showed that the NF and RO processes have a high percentage of TDS removal at all pressures. The NF and RO membranes showed very high efficiency in the reduction of TDS. The RO system needs more energy than the NF system.