Chemical variability of groundwater samples collected from a coal seam gas exploration well, Maramarua, New Zealand

► Hydrochemical variations due to CO2 degassing in CSG Water can be up to 33%. ► CaCO3, ZnCO3, and FeCO3 are minerals likely to precipitate with CO2 degassing. ► pCO2 in the aquifer can be up to 2 orders of magnitude higher than at the surface. ► 16.5% of chemical variations reflect the mixing of water of varying composition. ► Using low drying temperatures (<180 °C) can result in an overestimation (10%) of TDS.