Water levels in the dams supplying Istanbul have fallen below 40%, a threshold the city's reservoirs have dipped under in September only three times in the past decade, according to data from the Istanbul Water and Sewerage Administration (İSKİ).
As of September 18, average occupancy across the dams serving Türkiye's largest city stood at 38.03%, equal to about 330.03 million cubic metres of water. The combined storage capacity of the city's dams and reservoirs is around 868.68 million cubic metres.
On the same date in previous years, levels had been below 40% only twice in the last decade: in 2023, when they stood at 25.28%, and in 2025, when they were 33.49%.
Rainfall declining
İSKİ data show that rainfall in the dam catchment areas has decreased steadily in recent years. Annual precipitation was 852.64 kilograms per square metre in 2023, falling to 709.27 in 2024, 619.92 in 2025 and 540.49 so far in 2026.
Güven Özdemir, a professor of meteorology at Istanbul Aydın University, said that less rain directly translates into less water flowing into the reservoirs. He noted that hot weather also increases evaporation and moisture loss from soil and vegetation, while pushing up demand from households and for irrigating parks and green spaces.
Özdemir also pointed out that heavy downpours over a short period do not refill reservoirs as effectively as steady, regular rainfall, since much of the water runs off. He said precipitation over the coming autumn and winter would be decisive for the city's water resources, and urged residents to use water carefully during dry, hot spells.
A recurring concern
Istanbul, home to more than 15 million people, relies on a network of reservoirs on both the European and Asian sides of the city. Low reservoir levels have repeatedly triggered public concern in recent years, especially in late summer and autumn before winter rains arrive.
Several Turkish regions have faced drought conditions in recent years, and authorities have increasingly promoted water-saving measures.
Sources
Photo: aachim3 (https://www.panoramio.com/user/2349392?with_phot… / CC BY 3.0, via Wikimedia Commons
