A system for the exploitation of geothermal heat and for conveying and decontaminating ground water is disclosed. The system comprises a main pipe (20), arranged in a pit (10) of well and is subdivided into an upper and a lower part by a transverse seal (21). The transverse seal has an opening in which a pump (22) is arranged which delivers water from the lower part of the main pipe. The pump is connected to a delivery pipe (30) which is connected to an overground closed circuit. The closed circuit at its other end leads to the upper part of the main pipe and the main pipe has through openings (23) towards the surroundings upstream and downstream of the transverse seal. The main pipe is surrounded by a porous bed which surrounds the hollow space of the pit around the main pipe. The porous bed is interrupted by a sealing material (12) at the level of the transverse seal so that the porous bed is hydraulically interrupted. The use of the system is also described.