Faults related to the neotectonic stress regime of northwest Turkey permit the rise and outflow of thermal waters in two different districts in Bursa city. Based on their geographical, physical and chemical characterization, two different circulation systems with maximal spring temperatures of 82 degrees C (TDS = 1207 mg/L) and 46 degrees C (TDS = 504 mg/L) can be distinguished. Isotopic data indicate different local recharge areas and residence times of at least 50 years. Water temperatures at depth are about 110 and 50 degrees C. Calcite dissolution and silicate hydrolysis are the dominant water-rock interactions. The dominant processes that affect both deep groundwater circulation systems are: mixing with shallow groundwater, loss of energy by heat conduction, and interaction with gases from mantle, crust and atmosphere.