The idea of implementing ancient water and wastewater technologies in the developing world is a persuasive one, since ancient systems had many features which would constitute sustainable and decentralised water and sanitation (WATSAN) provision in contemporary terminology. Latest figures indicate 2.6 billion people do not use improved sanitation and 1.1 billion practise open defecation, thus there is a huge need for sustainable and cost-effective WATSAN facilities, particularly in cities of the developing world. The objective of this study was to discuss and evaluate the applicability of selected ancient WATSAN systems for the contemporary developing world. Selected WATSAN systems in ancient Mesopotamia, the Indus Valley, Egypt, Greece, Rom...