Abstract: The apparatus treats storm water and includes a cylindrical basket that has a housing with a circumferentially extending air slot near the base of the housing. The basket contains an annular bed of absorbent material surrounded by a filter cartridge. Water flows radially inward through the filter and the bed into a cylindrical inner drainage space which has an outlet at its lower end, covered by a float valve. The drainage space is also in fluid communication with a one-way valve that allows air to pass from the housing into the environment. During operation, the float valve lifts when the water level rises and air is expelled from the drainage space through the one-way valve. As a result, water is continuously siphoned through the basket apparatus. When the water level drops, air enters through the air inlet slot of the housing and rises in turbulent fashion along the filter, scouring the filter and dislodging particulates.