Surface water (main rivers; availability since 1950)
The annual average precipitation in Turkey is approximately 574 mm, which equates to about 450 billion cubic metres (BCM) of water. Surface water potential that can be used for various purposes averages 94 BCM/yr under today’s technical and economic conditions. Turkey’s consumable surface and groundwater potential is 112 BCM/yr, of which 57 BCM is utilized (Table 1).
Table 1: Turkey’s water potential.
|Mean annual precipitation (mm/yr)||574|
|Area of Turkey (km2)||783,577|
|Total volume of water (BCM)||450|
|Annual runoff (BCM)||186|
|Usable surface water (BCM)||94|
|Annual abstracted groundwater (BCM)||18|
|Total usable water potential (BCM)||112|
Turkey is divided into 25 hydrological basins. These river basins each have a different catchment size and a wide range of annual precipitation, evaporation and surface runoff variables. As a result, river discharges are unpredictable. Within Turkey’s borders, 16 rivers rise in the mountains and flow into the Marmara Sea, Mediterranean Sea, Black Sea and Aegean Sea. The Konya Basin, Akarçay Basin, Burdur Lakes and Lake Van are closed basins, meaning they have no outflow to the sea. The Maritza, Orontes (Asi), Araks-Kura, Euphrates-Tigris and Çoruh basins are the primary transboundary basins.
According to studies carried out by the General Directorate of Nature Conservation and National Parks, Turkey has 320 natural lakes. Some of these are seasonal, filling up with winter precipitation and then drying out in the summer due to a lack of precipitation. The largest lakes include Lake Van at 3,713 square kilometres (km2), Salt Lake (1,300 km2), Beyşehir Lake (656 km2) and Egirdir Lake (482 km2).
Groundwater (main aquifers/springs; availability since 1950)
As mentioned above, Turkey’s total usable water potential is 112 BCM, of which 94 BCM is surface water and 18 BCM is groundwater. Turkey’s groundwater operating reserves total 18 BCM, although only 16.62 BCM have been allocated as follows: 11.21 BCM as agricultural irrigation (individual irrigation, public and cooperatives), 1.49 BCM as industrial water and 3.92 BCM as drinking water.
There were 369,054 certified wells as of the end of 2019, with 38,071 for drinking, 17,904 for industrial use and 313,079 for irrigation.
Groundwater resources are governed by the Groundwater Law of 1962. In accordance with this law, groundwater resources fall under the jurisdiction of the state. The protection, research, registration and use of these waters are also covered by this law. Every well has to be registered, but unlicensed well digging is hard to control. As in other places around the world, groundwater resources in Turkey are used for irrigation to a great extent.
In order to monitor groundwater extractions and prevent overuse, a groundwater measuring regulation was enacted in 2011. Effective implementation of this regulation faces several challenges such as the existence of unlicensed wells, the difficulty of preventing illegal use of wells and changing climate and precipitation patterns. Despite these challenges, the regulation is a major step forward in the protection and management of groundwater resources.
Non-conventional sources (desalination; wastewater reuse; rainwater harvesting)
A growing population and increasing demand coupled with climate change impacts are putting pressure on already scarce water resources. Research is currently being conducted on the use of non-conventional water resources. Particular focus is placed on reusing wastewater in agriculture, improving water efficiency in the agricultural sector, drainage water use and saline water use in agriculture, rainwater harvesting and small-scale desalination projects (seawater or brackish water).
In a country where agriculture accounts for more than 73% of the country’s water use, significant efforts should be made to improve efficiency, as the potential for water conservation is far greater in agriculture than in other water-using sectors. Reduced conveyance losses and improved irrigation efficiency, for example, can result in water savings in the irrigation sector.
In other areas, a rainwater collection system is now required for buildings constructed on parcels larger than 2,000 square metres (m2), following the Ministry of Environment and Urbanization’s amendment of the Planned Areas Zoning Regulation, which was published in the Official Gazette on 21 January 2021.
Total water availability and per capita availability
Turkey’s mean annual precipitation is 574 mm, which amounts to 450 BCM of water. Of this, 219 BCM evaporate and 45 BCM leak into aquifers and thus are lost from the water budget. Of the total amount, 181 BCM are mixed with rivers and lakes as surface water. While 6 BCM come from neighbouring countries, 41 BCM are retrieved from groundwater contributing to surface water, and this amount is included in the water budget. Turkey’s overall water potential is 231 BCM, but given the country’s economic and technical constraints, the annual exploitable water potential has been calculated as less than half that, at 112 BCM.[
 Topcu, S, Kibaroglu, A and Kadirbeyoglu, Z, 2019. ‘Turkey.’ In: Molle, F, Sanchis-Ibor, C and Avellà-Reus, L (eds). Irrigation in the Mediterranean. Global Issues in Water Policy, vol 22. Springer, Cham.
 DSİ (Devlet Su İşleri), 2022. http://www.dsi.gov.tr/.
 DSİ (Devlet Su İşleri), 2018. http://www.dsi.gov.tr/.
 AA, 2020. ‘AA, 2020. ‘Controlled consumption requirement for groundwater.’ Published 21 March 2020.’ Published 21 March 2020.
 Yeraltı Suları Hakkında Kanun (Law on Groundwater), 2011. DSİ Yeraltısuları Teknik Yönetmeliğinde Değişiklik Yapılmasına Dair Yönetmelik. Official Gazette, 7 June 2011, No. 27957.
 Ministry of Environment and Urbanization, 2017. Regulation about rainwater collection, storage and discharge systems. Official Gazette, 23 June 2017, No. 30105.
 DSİ (Devlet Su İşleri), 2018. www.dsi.gov.tr.
 DSİ (Devlet Su İşleri), 2022. www.dsi.gov.tr.
 Ministry of Environment and Urbanization, 2021. https://www.resmigazete.gov.tr/eskiler/2021/07/20210711-1.htm#:~:text=%E2%80%9Ca)%202000%20m%C2%B2’den,suyu%20toplama%20sistemi%20i%C3%A7ermesi%20zorunludur.
 DSİ (Devlet Su İşleri), 2018.www.dsi.gov.tr.