This study provides a comprehensive overview of consequences of geothermal systems in shallow aquifers. The authors conclude there is still a lack of knowledge on long-term environmental consequences. Due to local differences in geology and hydrogeology as well as technical requirements, the authors recommended that is addition to static regulations—such as fixed and absolute temperature thresholds—flexible temperature limits for heating and cooling the groundwater and subsurface should be defined. The limits should be oriented on previously undisturbed temperatures, and chemical, physical and biological conditions of aquifers. Based on these findings, recommendations for a sustainable policy for shallow geothermal systems are provided, including a potential legal framework for a sustainable use.