Provided are water treatment apparatus and method for controlling water treatment apparatus. The water treatment apparatus includes a filtering unit including a deionizing filter removing total dissolved solids contained in inflow water by an application of power, a water output unit outputting water filtered by the filtering unit; and a control unit controlling power that is applied to the deionizing filter to control total dissolved solids (TDS) contained in water filtered by the deionizing filter, or a reduction rate of total dissolved solids by the deionizing filter.