Transportable waste water treatment unit for purifying waste water, comprising - a box-shaped, watertight transport container which is open at its upper side , - a supply device for supplying waste water into the transport container , - a discharge device for discharging treated waste water, - a waste water treatment region provided in the transport container , which is provided with a granular substrate , and - reed plants suitable for decomposing impurities in the waste water and planted on the substrate , wherein the substrate is built up in layers and at least one layer contains a porous, light-weight substrate , characterised in that the waste water treatment region comprises at least two partially separated waste water treatment sections , in that the supply device for the waste water comprises at least one inlet which is arranged above the substrate , in that the supply device comprises a first inlet for the first waste water treatment section and a second inlet for the second waste water treatment section , in that the discharge device comprises at least one outlet element running horizontally in the substrate and connected to a discharge line which leads out of the transport container in order to receive and discharge the purified waste water, in that a truncated pyramid-shaped impact element is arranged on the substrate below the inlet , wherein the waste water passes through a region of ambient air before impacting on the truncated pyramid-shaped impact element , in that the first inlet and the second inlet each open out above the truncated pyramid-shaped impact element , and in that the outlet element is arranged in the lower substrate layer. - a box-shaped, watertight transport container which is open at its upper side , - a supply device for supplying waste water into the transport container , - a discharge device for discharging treated waste water, - a waste water treatment region provided in the transport container , which is provided with a granular substrate , and - reed plants suitable for decomposing impurities in the waste water and planted on the substrate , wherein the substrate is built up in layers and at least one layer contains a porous, light-weight substrate , characterised in that the waste water treatment region comprises at least two partially separated waste water treatment sections , in that the supply device for the waste water comprises at least one inlet which is arranged above the substrate , in that the supply device comprises a first inlet for the first waste water treatment section and a second inlet for the second waste water treatment section , in that the discharge device comprises at least one outlet element running horizontally in the substrate and connected to a discharge line which leads out of the transport container in order to receive and discharge the purified waste water, in that a truncated pyramid-shaped impact element is arranged on the substrate below the inlet , wherein the waste water passes through a region of ambient air before impacting on the truncated pyramid-shaped impact element , in that the first inlet and the second inlet each open out above the truncated pyramid-shaped impact element , and in that the outlet element is arranged in the lower substrate layer. <EOS>