"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 per cent 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.
The nine billion mark is widely projected to be reached from about 2040.
More From This Section
"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.
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.
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 per cent of it locked up in ice and permanent snow cover.
Thirty per cent of freshwater is stored underground in groundwater, which constitutes 97 per cent of all freshwater potentially available for human use.
About 0.3 percent is found in lakes and rivers.