The majority of people on Earth people will face severe water shortages within a generation or two if pollution and waste continues unabated, scientists warned at a conference in Bonn Friday.

"This handicap will be self-inflicted and is, we believe entirely avoidable," read a document entitled The Bonn Declaration issued at the close of the four-day international huddle.

The conference sought to assess the evidence of Man's impact on freshwater resources, which constitute only 2.5 percent of the total volume of water on Earth.

Currently, an estimated third of the world's seven million people has limited access to adequate fresh water, according to conference delegates.

"In the short span of one or two generations, the majority of the nine billion people on Earth will be living under the handicap of severe pressure on fresh water," said the declaration.

The nine billion mark is widely projected to be reached from about 2040.

"We are flying the red flag out of our conference here," Charles Vorosmarty, co-chairman of the Global Water System Project research body that hosted the meeting, said in a teleconference from Bonn.

"These self-inflicted wounds have long-term legacy effects that are not easy to turn around."

The declaration points out that humanity uses an area the size of South America to grow crops and another the size of Africa to raise livestock.

Two-thirds of major river deltas are sinking due to groundwater extraction, and tens of thousands of large dams are distorting natural river flows on which ecosystems have depended for millennia.

Much damage is being done by river pollution from sewer drainage or agricultural fertiliser and pesticide use.

Already, about a billion people around the world are dependent on finite water supplies being depleted at a fast rate, said Vorosmarty, who made a plea for more financial and technical resources for research.

"We're not making the requisite commitments to creating observational networks and satellite systems that can measure the state of water," he said.

"Increasingly, we are flying blind and finding it very difficult to figure where we are and where we're going and whether the things we are doing are making a difference."

UN-Water, a coordinating body for water efforts by UN groups, says Earth has about 35 million cubic kilometres (eight million cubic miles) of fresh water -- 70 percent of it locked up in ice and permanent snow cover.

Thirty percent of freshwater is stored underground in groundwater, which constitutes 97 percent of all freshwater potentially available for human use.

About 0.3 percent is found in lakes and rivers.

Experts say some 3,800 cubic kilometres of fresh water are extracted from aquatic ecosystems around the world each year, partly as a result of global warming.