Background: Quality control of drinking water is important for healthy consumers. Having a high total dissolved solid (TDS) in water causes a salty taste. Reverse osmosis is one among the membrane processing methods currently used for lowering TDS in water. As during the recent years several desalination plants were set into operation by private sectors in Kashan, the study was carried out for the evaluation of the quality control of inlet and outlet water of the mentioned plants.

Materials and Methods: This cross-sectional descriptive study was carried out using samples taken from the inlet and outlet water of plants during a six-month period in summer and winter seasons of the year 2008. A total number of 128 samples taken from 16 desalination plants were analyzed for water chemical quality.

Result: The average concentration of chemical parameters in treated water were: TDS= 245, total hardness=118, nitrate=2.5 mg/l, fluoride=0.2 mg/l, sulfate=24 mg/l, chloride=63 mg/l and pH range = 6.8-7.

Conclusion: Based on findings on desalinated water, except for fluoride, other parameters were in accordance to the optimum concentration for drinking water. For the prevention of dental caries, addition of fluoride should be considered in future program. While pH of outlet water was relatively decreased with respect to the raw water, but none of them were compatible with drinking water standards.