Abstract: The present invention relates to a device for creating a reaction zone in an aquifer, for circulating and purifying ground and raw water, in particular for tap water use, which aquifer comprises satellite wells and at least one extraction well wherein each satellite well comprises at least two, essentially vertical water conducting sections separated from each other in substantially vertical longitudinal direction, and having at least two geohydrologic zones, whereby said zones are arranged to alternating emit water to the surrounding, and receive water coming from the outside surrounding, respectively, whereby adjacent wells are arranged for opposite flows so that substantially horizontal flows are obtained in a water leading layer, in which layer the wells have been placed between adjacent wells, and whereby the water of at least one section is arranged to be pumped in one direction from below and upward, and at least in one vertical section, form above and downward, respectively, and to be lead out through