The process includes the creating in of an aquifer an oxidation and precipitation zone (or a reduction zone) between a number of injection wells arranged around one or more extraction wells for purified water. The zone desired is created intermittently between each pair of adjacent injection wells by (i) introducing oxygen, oxygen-containing gas or an oxygen-releasing substance (or an oxygen consuming substance) into the water in both two wells, and (ii) pumping the water in one well from below upwards while pumping the water in the other well from above downwards, where by a circulation circuit is formed in the aquifer between the wells. The device for carring out said process comprises an outer tube (1), sealing means (2), an inner tube member (3), a transversal wall (4) with a central opening and elongation tube (5), an inner flow pipe (6) and conduits (7, 8) for suplly of air.
