In this study environmental radioisotopes of water (³H and ¹⁴C) were used to determine the residence time of thermal waters. The temperature of geothermal waters was found to be uniform (57.6 °C ± 0.75 °C) with similar field alkalinity and pH values. The δ¹³C values of thermal water ranged between − 21.3 and − 18.75‰, which clearly reflect no/minimum contribution of carbonate minerals to the system. Environmental tritium concentration was found to be very low in these thermal waters indicating insignificant recharge from modern sources. The Pearson modelled ¹⁴C ages were found to vary from 4964 to 17,714 years.