Abstract: Method for operating a water system (10). The water system (10) comprises a fresh water subsystem (11) being configured to provide fresh water to water consumers (13, 14, 15, 16, 17, 19), wherein first water consumers (13, 14) generate black water as waste water, and wherein second water consumers (15, 16, 17, 18, 19) generate grey water as waste water. The water system (10) comprises a waste water subsystem (12) being configured to receive the waste water from the water consumers (13, 14, 15, 16, 17, 19). The waste water sub system (12) comprises a waste water diverter (23) being configured to provide in a black water status of the waste water diverter (23) waste water to a drain (24) thereby treating waste water as black water, and provide in a grey water status of the waste water diverter (23) waste water to a grey water tank (22) thereby treating waste water as grey water.