Scientists at the World Water Week conference which began on Sunday in Stockholm said that ignorance and complacency were widespread in wealthier countries.

"I don't know what will shake these regions out of complacency other than the fact there will be droughts, pestilence and wars that break out over water rights," said Mitsch, professor of natural resources at Ohio State University.

Mitsch told Reuters potential flashpoints included the Middle East.

"Continuing on our present path will mean more conflict," a report by International Water Management Institute (IWMI) said.

With the world's population growing at exponential rates there was extreme pressure on water supplies to provide drinking water and food, said scientists at the Stockholm gathering.

"In 2025 we will have another two billion people to feed and 95 percent of these will be in urban areas," said Professor Jan Lundqvist of Stockholm International Water Institute.

The answer was sustained investment in infrastructure.

An estimated $80 billion was invested each year in the water sector, but this needed to at least double, said Professor Frank Rijsberman, the IWMI's director general.

"I think if I look at the numbers I can't immediately see a way out over the next few years," said IWMI report co-author Dr David Molden. "I think we will reach a real crisis."