Embodiments of the invention provide a twin tank water treatment system and method. The water treatment system includes first tank with a first set of sensors and a first resin bed, a second tank with a second set of sensors and a second resin bed, and a valve assembly with a flow meter and a controller in communication with the first set of sensors, the second set of sensors, and the flow meter. The method includes determining when the resin beds are exhausted based on input from the flow meter, the sensors, and a water hardness setting.