The Aral Sea has shrunk by 90% in recent decades
The leaders of the five Central Asian states have failed to agree on the best way to share their water.
They signed a compromise statement that did not mention water sharing, concentrating instead on the decline in the level of the Aral Sea.
Correspondents say that a deal on water usage is key to regional stability.
Tajikistan and Kyrgyzstan hold 80% of the region's water, but much of this is needed in the three states downstream, which are semi-arid.
Uzbekistan, Turkmenistan and Kazakhstan rely on water from their neighbours for their important cotton industries, as well as for agriculture.
In Soviet times a system of exchange enabled the five states to share water and energy resources such as electricity and gas.
But this barter scheme is no longer active and the five states have been unable to devise a new one.
The Central Asian leaders have a poor history of co-operation, according to the BBC's Central Asian correspondent Rayhan Demytrie.
They meet infrequently and usually on the sidelines of other events.
But water allocation is becoming an increasingly pressing issue, and drought and overuse have caused an ecological disaster in the Aral Sea, which has shrunk by 90% in recent decades.
Tajikistan and Kyrgyzstan, which suffer most from lack of electricity during the cold winters, have long been pursuing the construction of hydropower plants.
But Uzbekistan fiercely opposes these projects, saying the construction of hydropower stations and new dams would reduce the flow of water for cotton irrigation downstream.