Abstract: The present invention relates to a method for decreasing the contents of metals, metalloids, nitrate and nitrite, respectively, in raw water flowing through a basin (1), whereby water containing either oxygen, oxygen-releasing substances, naturally occurring micro-organisms and/or substrates therefore is intermittently introduced to the basin (1) through horizontally arranged infiltration/extraction means (2) above and below the injection pipes of raw water, and by alternating the withdrawal and infiltration of conditioned water between the horizontal means so that essentially a vertical flow of water is created between these means, thereby creating a reaction zone for purification of raw water before it reaches the central extraction well. The water to be purified is fed into the basin by horizontally arranged feeding pipes (5) and the extraction of purified water from said at least one extraction well (3) is such that a substantially negative pressure is created around said at least one extraction well (3).

Abstract: The present invention relates to a method for decreasing the contents of metals, metalloids, nitrate and nitrite, respectively, in raw water flowing through a basin (1), whereby water containing either oxygen, oxygen-releasing substances, naturally occurring micro-organisms and/or substrates therefore is intermittently introduced to the basin (1) through horizontally arranged infiltration/extraction means (2) above and below the injection pipes of raw water, and by alternating the withdrawal and infiltration of conditioned water between the horizontal means so that essentially a vertical flow of water is created between these means, thereby creating a reaction zone for purification of raw water before it reaches the central extraction well. The water to be purified is fed into the basin by horizontally arranged feeding pipes (5) and the extraction of purified water from said at least one extraction well (3) is such that a substantially negative pressure is created around said at least one extraction well (3).