Water quality in drinking water reservoirs of a megacity, Istanbul

Providing clean water at relevant quality and quantity is a challenge that regulatory authorities have to face in metropolitan cities that seem to dev elop at their limits of sustainability. Istanbul strives to face such a cha llenge for its population of over 10 million, through six surface water res ources. Two approaches of classification for the reservoirs are presented, one based on current regulations and an alternative based on a more detaile d classification. The results have shown that nutrient control is the prima ry issue, and one of the reservoirs has already exceeded the limits of bein g eutrophic, one is at mesotrophic conditions, and the remaining four are a t the limit of being eutrophic, indicating the significance of making the c orrect decision and taking pertinent measures for management and control. I t has been observed that the only mesotrophic resource, which also has the best general quality class, has no industry and a very low population densi ty, whereas the one that is already eutrophic is also the one with the lowe st quality class, has the highest population density, and has the greatest percentage of urban land use within its watershed.