Abstract Hydrogeochemical investigations of groundwater in Torbat-Zaveh plain have been carried out to assess the water quality for drinking and irrigation purposes. In this study, 190 groundwater samples were collected and analyzed for physicochemical parameters and major ion concentrations. The abundance of major cations and anions was in the following order: Na+ > Mg2+ > Ca2+ > K+, and Cl− > SO2−4 > HCO−3 > CO2−3. As a result, alkaline element (Na+) exceeds alkaline earth elements (Mg2+ and Ca2+), and strong acids (Cl− and SO2−4) dominate weak acids (HCO−3 and CO2−3) in majority of the groundwater samples. Statistical analyses including Spearman correlation coefficients and factor analysis display good correlation between physicochemical parameters (EC, TDS and TH) and Na+, Mg2+, Ca2+, Cl− and SO2−4. The results display that rock-weathering interactions and ion-exchange processes play important role in controlling groundwater chemistry. Saturation index values also indicate that water chemistry is significantly affected by carbonate minerals such as calcite, aragonite and dolomite. US Salinity Laboratory(USSL) and Wilcox diagrams together with permeability index values reveal that most of the groundwater samples are suitable for irrigation purpose. However, in some regions, the water samples do not indicate required irrigational quality.

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