Turkmenistan's territory is covered for 80% by the vast Karakum Desert. In the southwest, along the border with Iran, and in the east, along the border with Uzbekistan, lie some mountain ranges. The cultivable area constitutes between 4% and 14 % of the country.
Internal river runoff originating in the country is negligible, with an estimated 1 km³ per year. There are only some small, internal rivers in the Kopetdag mountains at the country's southern border. Small transboundary rivers are the Atrek flowing from Iran, the Murghab from Afghanistan and the Tedzhen (flowing from Afghanistan through Iran into Turkmenistan). The Amu Darya provides almost 90% of the country's water via the Karakum Canal, which is the largest and most important water infrastructure in Turkmenistan. It runs from the border with Uzbekistan across the country to the western regions near the Caspian Sea. With a length of more than 1 300 km, it is the longest canal in the world. Further downstream in the north of the country, the oasis region of Dashoguz is fed by the Tuyamuyun reservoir located at the border of Uzbek territory. Furthermore, 18 smaller reservoirs were constructed mainly for irrigation purposes, with a total capacity of 2.89 km³. The largest reservoir is the Hauz-Khan reservoir on the Karakum Canal, with a capacity of 0.875 km³.
About 80 artificial drainage lakes were created by the outflow of salty drainage waters from irrigated fields. The largest one is the Saragamysh Lake (8 km³), located about 200 km southwest from the Aral Sea. It was formed in 1971 as a result of the flooding of several small lakes in the Sarykamysh depression, which were periodically filled by Amu Darya waters, and since then has become a large drainage water body, used as a discharge collector of salty irrigation water. In 2009, the Turkmen government started the construction of the Altyn Asyr Lake (Golden Age Lake), later renamed Grand Turkmen Lake, in the Karashor salt depression in the northern part of the country (about 350 km north of the capital Ashgabat). Old riverbeds and new canals with a total length of more than 1 000 km are expected to carry drainage water from different parts of the country that currently is discharged either back into the Amu Darya or into the Sarygamysh Lake. Once filled, the Grand Turkmen Lake is expected to be 103 km long and 18.6 km wide, with a capacity of 132 km³ and a surface of about 1 916 km². The government plans to develop it into a recreational zone, with some of its waters used to irrigate new pastures and orchards. However, experts have predicted the lake would have negative environmental effects and would reduce return water flows into the Amu Darya.
Turkmenistan possesses the world's fourth-largest reserves of natural gas and hardly any arable land. Consequently, the economic significance of agriculture is limited to 12% of the GDP (2009). However, more than half of the population lives in rural areas, and 32% (2004) are employed in agriculture. As in the other Central Asian states, irrigation is the main water consuming sector, with about 92%. Virtually the entire cultivated area is irrigated. An extensive network of canals with a total length of about 39 000 km have been been built, most of which are unlined, inefficient earthen canals. During Soviet times, the emphasis was on cotton cultivation. After independence, irrigation areas were expanded in order to grow more food crops and increase self-sufficiency.
There is a little hydropower potential in the country (estimated at 5.8 GWh), but only about 0.7 GWh (1993) is produced. Given the rich hydrocarbon resources, there is no interest in its exploration.
Due to its extremely arid climate, water is a critical resource for the country. This was already acknowledged in an old Turkmen proverb saying: «A drop of water is a grain of gold», which is also the motto of a national holiday celebrated annually on the first Sunday in April.[Kostianoy et al. 2011, Sehring 2002, UNDP 2010, WDI, AQUASTAT.]