This study reports physicochemical characteristics and their sources in groundwater in Thirupathur region in Tamil Nadu, India. For this purpose, groundwater samples were collected and analysed using standard methods. A wide seasonal variation was showed for the majority of the samples; higher concentration was observed in the pre-monsoon season. Concentration of fluoride was quite alarming in many locations. Groundwater is found to be dominated by Na+, Ca+, HCO3 and Cl−. Gibbs plot showed the dominance of rock–water interaction. Geology of the area in comparison with the results obtained in the chemical cross plots showed the dominance of silicate weathering, with a minor contribution from the cation exchange. Other processes such as evaporation dissolution of carbonate and gypsum were proved to be ineffective. However, dissolution of fluoride minerals present in the geological formation is the major source of fluoride in groundwater.
