Providing clean water at relevant quality and quantity is a challenge that regulatory authorities have to face in metropolitan cities that seem to develop at their limits of sustainability. Istanbul strives to face such a challenge for its population of over 10 million, through six surface water resources.
Nearly all of Istanbul’s drinking water (97%) comes from surface water collected in reservoirs. Its most important water sources are the Omerli-Darlik system on the Asian side and the Terkos-Alibeykoy system on the European side. Both systems consist of dams, reservoirs, water treatment plants and pipelines. Many of the reservoirs that supply Istanbul are located within the metropolitan area and are exposed to pollution from settlements without adequate sanitation.