A water treatment apparatus including a series of pairs of water filtration cells of an upwelling type. Each cell of each pair has a longitudinally extending water conduit in fluid communication between an upper and a lower end of each cell. The first cell of each pair is a fluidized bed type containing a biologically active media, the water entering a bottom of this cell upwelling through the biologically active media to discharge from a discharge port at or near the top of the first cell. The second cell of each pair has the upper end of its water conduit in fluid communication with the discharge port of the paired first cell and contains media which removes nitrates from the water entering and upwelling through the nitrate removing media for discharge from the second cell.