Abstract: A multistage water purification method in which water purifiers are arranged in stages in water regions of different depths. Air is made to ascend intermittently in each depth region by the water purifier to stir and mix the water with the air to enrich the water in oxygen thereby to purify the water. Disclosed also is a water purification apparatus for carrying out the water purification method. The apparatus includes an upper stage water purifier having a buoyancy chamber, a pumping sleeve and water suction tubes, and at least one lower stage water purifier having an arcuate deflector, a pumping sleeve and an air chamber. The upper stage water purifier and the lower stage water purifier are connected in series in vertical alignment or, alternatively, offset in the horizontal direction from each other.