This paper investigates groundwater changes in the Kashan Basin quantitatively and qualitatively. According to the data obtained from 53 observation wells, it is found that the mean water table is decreased about 7.93 m between 1990 and 2006, indicating a mean water table decline of 0.496 m/year. To study groundwater quality, 21 samples are analyzed for their physicochemical characteristics such as pH, hardness, chloride (CI), electrical conductivity (EC) and total dissolved solid (TDS) values. Comparing the results with drinking water quality standards issued by World Health Organization (WHO), it is found that most of the water samples are not potable. Hydrochemical facies using Piper diagram indicate that in most part of this basin, the chemical character of water is dominated by NaCl. However, Na% values indicate that just 53% of samples are permissible for irrigation. The chloride-bicarbonate ratios reveal that salt lake intrusion to this basin is the main source of salinity. It is also found that functional relationships between EC and Cl are logarithmic. (C) 2010 Elsevier B.V. All rights reserved.