The quality of groundwater and spring water for use in open-loop type groundwater-based heat pump system in the Pacific Ocean coast of Aomori Prefecture was evaluated on the basis of the water quality guidelines for refrigeration and air conditioning equipment. The water-quality parameter values for the groundwater and spring water were considerably higher than the corresponding standard values; the difference between the actual and standard values was highest for the free carbon dioxide concentration, followed by the silica concentration. A significant reason for the high free carbon dioxide levels is assumed to be the generation of CO₂ due to the decomposition of organic matter in the subsurface environment. The development of open-loop type groundwater-based heat pump system in this study area in the future will be a significant challenge as system durability is expected to be low because of corrosion and silica-scale problems.