The invention relates to a method for washing clothes, especially working clothes, in which the clothes are washed with a detergent and cleansing agent in an ordinary washing machine for commercial laundries and the waste water is processed by means of a membrane installation. The method is characterized in that the waste water is conducted via a nano-filtration membrane, and separated in a dirt-enriched concentrate and a dirt-depleted regenerated waste. The regenerated waste is fed back to the washing process. The water can be processed to a high degree of purity, so that it can be returned to the washing process without impeding the washing capacity of the installation.