A dishwasher is provided that advantageously enables reduction of the amount of water required during the rinsing cycle in order to thereby minimize operational costs and to improve environmental compatibility. A water preparation system has a water preparation container which can receive at least one part of the rinsing liquid used during operation of the dishwasher. The impurities contained in the rinsing liquid are at least partially biodegraded during a water preparation phase with the aid of microorganisms. By preparing and recycling at least one part of the used rinsing water, it is possible to reduce the requirement for fresh water. This enables the burden on the environment to be reduced since at least one part of the water used during the rinsing process is biologically cleansed while it is still in the dishwasher and the requirement for fresh water for the dishwasher is thus reduced.