A commercial dishwasher comprising spray nozzles for spraying liquid into a treatment region in the form of a treatment chamber or a treatment zone for treating items to be washed; at least two centrifugal pumps, which are arranged in series hydraulically one behind the other, for conveying liquid from the wash tank to the spray nozzles; a control device for alternatively operating only one centrifugal pump or at least two of the centrifugal pumps which are connected hydraulically one behind the other in series, in order to thus generate different liquid pressures.