HPA Director Yıldız : İstanbul’s  Water and Sanitation  Management Paradigm need to be shifted  

7 May 2021

HPA Director Dursun Yıldız  made a presentation about Water and Sanitation Management in İstanbul (Case study) at   HPA  International Webinar on: “21st Century, Water and Sanitation in Cities” on May 6, 2021

His presentation title was “How long can the current water supply management policy be sustainable for İstanbul’s Future “

In his presentation,he highlighted  following points in detail;

Nearly all of Istanbul's drinking water (97%) comes from surface water stored 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. Water quality is theoretically controlled by conservation zones around the reservoirs which limit construction and industrial activities in four concentric buffer zones with increasingly strict regulations the closer the zones are to the reservoirs[1],[2]

However, over time, the infrastructure in İstanbul failed to improve and ghetto neighborhoods made the distribution of services harder. The need for a new administration with broader authority and abilities was seen as İSİ failed to meet the increasing population's water and sewerage demands. The name of the new administration founded in 1981 is İstanbul Water and Sewerage Administration (İSKİ).

Because of the rapid population increase in Istanbul, additional water resources were needed. Therefore the Melen System was developed to cover the long-term water demand of İstanbul. The first stage supplying 268 million m3 was completed in 2007. A second and third stage is expected to bring a total of 1,180 billion m3 for all three phases to meet the water demand of the city until the year 2040, doubling the amount of water supplied before the Melen system. Also, a 5.5 km tunnel under the Bosporus  transfers water to the European side[3] According to monitoring by four metropolitan agencies drinking water quality is good, reportedly surpassing Turkish as well as EU standards. According to a 2004 survey, 35% of customers stated that they drink water from the tap, up from only 10% in 2000. During that period water quality had improved due to network repairs and the completion of new drinking water treatment plants.[4]

Although the data do not indicate a clear long-term declining trend in rainfall, extreme events – especially two-year droughts – seem more pronounced than in the past. In 2006, rainfall of 67 mm was the record low for the previous 50 years, a period during which the average was 257 mm per year. Furthermore, the water level in reservoirs serving the city plummeted to around 25% of full capacity in 2007 and 2008.ın 2020 rainfall was under the normal level and it continued in the 2021 water years resulting in the use of some dams in the European side of İstanbul. The total water volume rate in the dams dropped as of % 19.

Population and water resources are unevenly distributed throughout IstanbulAbout 60% of the water in Istanbul is on the Asian side. However, 65% of the population lives on the European side of the city. Due to the increase in population and changes in precipitation rates, the need for water has increased in recent years. Therefore, the idea of the Melen project was developed at the beginning of the 2000s,  It was aimed to bring water from Melen Creek, which is about 180 km away from Istanbul. The first water in Istanbul was launched in 2007 with the Melen Project. The Greater Melen  Project (GMP) is a large-scale interbasin water transfer project that provides domestic and industrial water requirements of Istanbul for 2040

Due to the increase in population and changes in precipitation rates by years, Istanbul faced a water shortage threat in 2007,2014, years. But partially completed Melen Project helped İstanbul to overcome these critical periods.

In the year 2019, annual total rainfall was lower than the mean value in İstanbul. This meteorological drought period has continued in 2020 and Istanbul entered the new water year 2021 with a very low water storage rate in the dam’s reservoir

In contrary to expectations, the meteorological drought period has continued in the last four months of the last year.  The total amount of water in the dam’s reservoir was decreased by 20% in total. Fortunately, precipitation started with a delay of 3 months and the amount of water in the dams started to increase in February 2021.

With this population and water use trend, Istanbul falls to water shortage when annual rainfall is lower than average level during consecutive two years.

 But it should be noted that, although the amount of rainfall in various years until 1994 was very low, it did not cause a serious water shortage. The water shortage occurred in 1994 due to increased population with 500 mm of precipitation for 2 consecutive years. Later, due to the rapid increase in the population and the low annual precipitation, water shortages occurred again in 2007, 2014, and 2020. However, the total occupancy rates in the dams increased up to 81% in April 2021, it was observed that this accumulated water volume rate tended to decrease over the previous years.

During these drought periods deficiency of water budget has always occurred in İstanbul West. The deficiency in the water budget of Istanbul West was provided from Melen and Yeşilçay systems.

Water has transferred to the European side with a 6 m diameter tunnel that goes 135 m below sea level crossing the two continents. This tunnel has a capacity of 3 million m3 of water per day.

Melen and Yeşilçay  System has partially served Istanbul since 2007. Since then most of the years' one-third of annual water demand was supplied by Melen and Yeşilçay System to Istanbul. But last year this rate was increased by 50 %.

The last part  of the Melen Water Supply  system, Melen Dam is expected to be completed   by the end of 2017  It would have a huge storage capacity of 694 million-cubic-meter that   equals 75 percent of the total capacity of all  İstanbul Dams

Although the dam construction to a large degree was completed in 2019, due to cracks as a result of insufficient ground reinforcement work, filling of the dam reservoir couldn't be started. Therefore the waters taken from  Melen River need to continue to be pumped with a large number of pumps, each having a maximum pressure height of 220 meters.

The total pressure height needed  to transfer 1,2 million m3/day  from Istanbul East to West is about 300 m

Although the water level was rising in the dams in February 2021, the Mayor of Istanbul Mr. Imamoğlu made a statement saying that we must implement water demand management rules, it is just time to start. But it was not executed properly.

While İstanbul is waiting for the completion of the Melen dam to avoid the threats of possible dry periods in coming years, other challenges come out.

If ıstanbul Canal will be implemented It will largely and seriously affect the Istanbul West water supply plan. Many existing water infrastructure and facilities will be disabled and rebuilt due to the construction of the Istanbul canal.

In addition, it is estimated that the additional population that will come to the residential areas in the zoning plans will reach 1.5 million people.

Authorized organizations planned some more dams on both sides of İstanbul to provide water for rising demand.

In contrary to the rising water demand part, additional dams planned in İstanbul west has a storage capacity of 120 million m3 while  Istanbul east has 422 million m3

Not only in İstanbul but also several metropolitan cities in the world,  transferring their additional water demand from other river basins are common.

But This global trend likely to create water allocation disputes between cities and regions. That means that in addition to international hydropolitics subnational hydropolitics will be needed soon


In 2021 Istanbul's wastewater system consisted of 14 990  km of sewers, 17 pumping stations, 67 wastewater treatment plants. 95% of the wastewater collected was being treated. Treated wastewaters are discharged into the Bosphorus. They are discharged into the lower layer, where the flow is towards the Black Sea in the North.

As of 2021, %, 2,5 percent of treated wastewater is reused in İstanbul.

Lessons Learned


  • Istanbul sets a good example to the challenges faced in water supply in heavily populated cities,
  • Right in time measures in water management  are vital to managing future risks
  • Problems caused by lack of implementation of water demand management  could be compensated by some  expensive  engineering solutions
  •  Water demand management needs to be implemented when water is available
  • Even though Istanbul has had water supply problems periodically, sustainable water governance to Istanbul has not been the subject of scientific and innovative management concepts.
  • The most important reason for this has been the policy of providing water to the rapidly increasing population.
  • The Istanbul Metropolitan Municipality has tried to meet the water demand of the increasing population with only a supply management concept
  • It resulted in water transfer from  other river basins with higher cost
  • In İstanbul rising water demand and supply management  trends point towards unsustainable use of water
  • This paradigm needs to be shifted

           The reuse, Reduce,Recycle, Recover approach is needed


İstanbul Canal Project, meteorological drought periods developed smart water technologies, and new water management concepts force paradigm shift in İstanbul.

Considering innovative  smart water management concepts Istanbul Water and Sanitation Governance  can be replanned as East and West İstanbul  taking into account reuse, reduce,recover, recycle of water


[1]  Ali Demirci and Anya Butt: Historical Overview and Current Trends in Istanbul's Water Supply Development, Globalization And Water Resources Management: The Changing Value of Water, August 6–8, Awra/Iwlri-University of Dundee International Specialty Conference 2001. Retrieved September 14, 2010.


[2]German) Şenda Kara and Frank Alleweldt:Trinwasserversorgung und Stadtexpansion:Der Fall Istanbul (Drinking Water Supply and Urban Expansion:The Case of Istanbul), in: Wasser - Abwasser 136 (1995), Nr. 7, pp.)

[3]  XIVst Regional Directorate of State Hydraulic Works -Istanbul. Retrieved September 14, 2010.

[4]  Altinbilek, Dogan. "Water Management in Istanbul". International Journal of Water Resources Development. 22 (2): 241–253. doi:10.1080/07900620600709563.

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