Wong Poh Poh, a professor at the National University of Singapore, told a regional conference that global warming was disrupting water flow patterns and increasing the severity of floods, droughts and storms — all of which reduce the availability of drinking water.

Prof. Wong said the UN Intergovernmental Panel on Climate Change found that as many as 2 billion people won’t have sufficient access to clean water by 2050. That figure is expected to rise to 3.2 billion by 2080 — nearly tripling the number who now do without it.

Reduced access to clean water, which refers to water that can be used for drinking, bathing or cooking, forces many villagers in poor countries to walk miles to reach supplies.

Others, including those living in urban shanties, suffer from diseases caused by drinking from unclean sources.

At the beginning of the decade, the World Health Organisation estimated that 1.1 billion people did not have sufficient access to clean water. Asia, home to more than 4 billion people, is the most vulnerable region, especially India and China, where booming populations have placed tremendous stress on water sources, said Wong, a member of the UN panel.

"In Asia, water distribution is uneven and large areas are under water stress. Climate change is going to exacerbate this scarcity," he told the two-day Asia Pacific Regional Water Conference attended by policy makers, government officials, academics, businessmen and consumer group representatives.