The present invention relates to an artificial aquifer for decreasing the contents of metals, metalloids, nitrate, nitrite, pesticides and organic micro contaminants in natural ground water or artificial infiltrated groundwater from surface water. The system comprising a basin of filling material creating a reaction zone, a feeding line, one or more satellite wells, at least one main well and a pumping well, whereby the feeding line is applied in the upper outer periphery of the basin and wherein the main well is connected to a pumping well via a bottom outflow provided with a regulating valve to maintain a given level of water in the aquifer. The invention further relates to a method for purifying water.