This paper presents a study of water management in Istanbul, a megacity with a population of 11.5 million. The population of Istanbul grew at almost twice the overall rate of the whole of Turkey because of a large in-migration. The projected water demand was underestimated and Istanbul experienced severe water shortages in the early 1990s. During the last decade US$ 3.6 billion of investments were made to improve and expand water and wastewater systems. Several large-scale water transmission projects were started. The percentage of treated wastewater increased from 10% to 95% within the same period. The unaccounted-for water rate has been reduced from 50% to 34%. Environmental protection measures have been put into effect to protect the watersheds of the water reservoirs. The 2002 Metropolis Award Winner Golden Horn Environment Protection Project is another example of environmental rehabilitation efforts undertaken in Istanbul.