In Istanbul, where daily water consumption averages around 3 million cubic meters, reservoir levels have continued to decline throughout October, despite a notable rise in rainfall.
Data from the Istanbul Water and Sewerage Administration (ISKI) reveals that reservoirs supplying the city received 93.49 millimeters of rainfall in October 2025. This represents the third-highest October rainfall total recorded over the past decade, following 2015 and 2020. However, despite this above-average precipitation, reservoir levels dropped significantly over the same period.
The combined water storage in Istanbul’s main reservoirs, including Ömerli, Darlık, Elmalı, Terkos, Alibey, Büyükçekmece, Sazlıdere, Istrancalar, Kazandere and Papuçdere, fell from an average fill rate of 28.49% on Oct. 1 to 22.96% by the end of the month, marking a monthly decline of 5.53%.
Meanwhile, the city’s daily water consumption remained high, reaching 3.14 million cubic meters in October. A substantial portion of the city’s supply, totaling approximately 36.87 million cubic meters for the month, was sourced from the Melen and Yeşilçay river systems, which serve as critical water regulators for Istanbul.
Professor Hüseyin Toros, an expert in climate science and meteorological engineering at Istanbul Technical University, highlighted that nationwide rainfall levels in October were above normal. He noted that the rainfall positively influenced reservoir water levels by slowing the rate of decline compared to previous months.
“From June onwards, reservoir depletion averaged 12%-13% per month. In October, the decline was reduced to 6%. While the reservoirs lost 1% of their volume every three days in the summer months, this rate slowed to 1% every six days in October,” Toros explained.
Despite this, the overall drop in reservoir levels underscores the ongoing challenge of meeting Istanbul’s growing water demand amid climate variability. Toros stressed the urgency of water conservation efforts, emphasizing that sustainable water management and behavioral changes at the individual level remain critical to securing the city’s water future.
With the Melen and Yeşilçay rivers identified as vital arteries supporting Istanbul’s water network, maintaining their flow and integrity is essential for the city’s resilience against seasonal fluctuations and long-term supply risks.
