Iran\\\'s groundwater hydrochemistry has not been well understood. In this study, Iran\\\'s groundwater hydrochemistry is evaluated using a rich, ground-trusted data sampled from 9,468 wells distributed across the country in 2011. Twelve groundwater quality parameters were analyzed in each sample, resulting in 113,616 parameters over the study period. Examination of anions-cations shows that concentrations of sodium, calcium, chloride, and sulphate are higher than the acceptable threshold for drinking-use suggested by the World Health Organization in about 40%, 21%, 25%, and 20% of the samples, respectively. The results of the water quality index reveal that most of the groundwater resources in the central, southern and eastern regions of Iran, which supply the majority of the domestic water for populated cities, do not meet the requirements for drinking-use. Although the groundwater in northern parts fulfills the requirements for irrigation-use, it is only suitable for irrigation of salinity-friendly crops in central, eastern and southern regions. Ionic types and hydrochemistry facies indicate the dominance of mix water type in 13 out of 30 of Iran\\\'s sub-basins, followed by sodium-chloride water type in nine sub-basins. Local geology and lithology are mainly attributed to the distribution of groundwater facies in Iran. In general, our findings reveal a distinctive relationship between Iran\\\'s geological-geomorphological features and hydrochemical facies/groundwater quality. The findings can be used in the formulation of new strategies and policies for Iran\\\'s groundwater quality management in the future.

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