Sodium-bicarbonate HCO3Na (sodic) groundwaters exist throughout southeastern West Siberia at approximate depths from 50300 m to 1.02.3 km in Mesozoic-Cenozoic sediments. They belong to five main types of fresh (I), brackish (II), high-pH low-saline (III), coal-related saline (IV), and carbonated (V) waters that differ in composition, as well as in depth and lateral extent. Waters of types I and II are of regional extent and common chemistry, while those of three other types have specific compositions and are restricted to local areas. Isotope data (18O, D, 13C) indicate that waters of all five types originated by the infiltration mechanism; type IV water has an enriched oxygen isotope composition; all water types except V have biogenic carbon sources. As shown by thermodynamic calculations, all HCO3Na waters are nonequilibrium with many primary aluminosilicate minerals bur are equilibrated with carbonates and clay minerals. The number of minerals equilibrated with these waters increases progressively from type I to IV with salinity and pH. The obtained data allow reconstructing the formation of sodic waters of different types in the context of the evolution in the system water rock gas organic matter. The formation scenario is the same for all types of water: dissolution of sedimentary aluminosilicate minerals which are not in equilibrium with the waters and concurrent precipitation of carbonates. Waters in the zone of slow water exchange at depths from 100 to 300 m acquire the HCO3Na compositions, with TDS >0.70.8 g/L and aH >7.6. The diversity of the waters results from difference in their residence time, even during the formation of HCO3Na chemistry (types I and II), and from environment effects: presence of inorganic CO2 (V) and organic carbon (IV) sources or their absence (III).