Water systems in civil aircraft, stimulated by passenger comfort needs, have grown to be a comprehensive and important part of aircraft engineering. In this article, following a review of the system types, the design features arc discussed in detail and emphasis has been placed on the functional and hygiene requirements, and on the need for simplicity and weight conservation. Attempts have been made to augment air‐borne water supplies by reclamation means, but these have not been too successful. Investigations should therefore continue into the ways and means of improving the utilization of existing ‘fixed’ capacity systems. Installation safety aspects are also discussed.