Evaluation of water treatment system's performance available in Bojnurd ciry during 2013

water treatment systems by reverse osmosis are treatment systems in consumer point. According to water quality in Bojnurd city and Consumers tend to use water treatment systems. This study was carried out for the evaluation of water treatment systems’ performance and compared with national standards.Method and Materials: This cross-sectional descriptive study was carried out using samples taken from the inlet and outlet water of plants during a seven-month period in winter until summer seasons of the year 2013. A total number of 66 samples taken from 6 plants were analyzed for water physical, chemical and microbial quality. Data were analyzed with SPPS 18 and presented with Kolmogorov–Smirnov and T-Test. According to the results the percentage of physical and chemical parameters in treated water for hardness, Alkalinity, Fluoride, TDS, Turbidity, EC, chloride, Na, K, Nitrate, Sulfate and Phosphate were all in acceptable level except for Fluoride and Mg. The average concentration of residual chlorine= 0.64 mg/l and pH range = 7.68. T-Test for total parameters except Phosphate were P<0.05. 5.41% of samples were contaminated by Total Coliforms and all samples by Clostridium perfringens but no fecal coliforms. Heterotrophic bacteria were lower than standards. Continuous control and monitoring of the quality of inlet and outlet water in desalination plants is necessary.