"Today more than one billion people the world over lack access to safe drinking water", Rakhmonov told delegates from around 50 countries.

The gradual drying up of the Aral Sea has left a 400-square-kilometre toxic wasteland threatening some three million local residents and "will cause climate change over a vast territory", Rakhmonov said.

Delegates from some 50 states around the world gathered for the key-note event in the "year of fresh water" declared by the United Nations on Tajikistan's initiative.

"All over the world both the quantity and quality of safe water are decreasing as a result of pollution, over-consumption and mismanagement ... each year more than two million children die from water-borne diseases", UN Secretary General Kofi Annan said in a written message to the conference.

The source of much of Central Asia's water, Tajikistan's complex network of dams and rivers has been severely degraded by years of neglect and and a civil war which followed the end of Soviet rule.

As a result clean water supplies are severely limited and around five million people in Tajikistan and neighbouring regions are threatened by the possible collapse of a vast natural dam at Lake Sarez formed in the early 20th century by an earthquake, Rakhmonov said.

"It has become quite evident that either single-handedly or with the support of all Central Asian states Tajikistan will not be able to deal with the threat of a humanitarian and ecological disaster (at the dam)", Rakhmonov said.

It is unclear how much the three-day conference will accomplish since several of Tajikistan's neighbors who face grave water-related problems are not sending high-level government officials to the event.

"The Central Asian nations still approach the issue purely as an engineering problem," the Kyrgyzstan office of the International Crisis Group wrote recently. "Each country has started to view the problem as a zero-sum game."

There are also worries that new demand for Central Asian water could come from neighbouring Afghanistan as it rebuilds its war-ravaged economy.

The UN's new World Water Development Report estimates that some 2.2 million people around the world died due to water-related diseases last year.

Partly due to global warming, well over two billion people will be suffering from water scarcity by the middle of this century, the report warns.

SPACE.WIRE