Abstract: A relatively compact and inexpensive technique for the two step decontamination of a liquid such as water is described. The liquid to be treated is propelled upwardly through a pair of vertically superposed, lower and upper chambers defined in a common treatment tank and separated by a liquid-permeable nozzle member. A first decontamination-removing substance, such as adsorbing material or an ion exchanger, is disposed in the lower chamber, while a second decontamination-removing substance such as activated charcoal is disposed in the upper chamber. The first substance, when spent, is propelled out of the lower chamber by a transport liquid, externally renewed, and recirculated back into the second chamber as a fresh charge by passing through a central pipe that extends through the upper chamber and the nozzle member to terminate in the lower chamber.