AFP - The World Water Forum, a seven-day arena aimed at addressing the planet's deepening crisis of freshwater, was launched here Monday, drawing record-breaking participation by politicians, specialists, corporate executives and activists.

The forum, held only every three years, will address problems of water scarcity, the risk of conflict as countries squabble over rivers, lakes and aquifers, and how to provide clean water and sanitation to billions.

The world's population, currently more than 6.5 billion, is expected to rise to nine billion by mid-century, placing further massive demands on water supplies that are already under strain.

According to the Organisation for Economic Cooperation and Development (OECD), the number of people living under severe water stress is expected to rise to 3.9 billion by 2030, amounting to nearly half the world's population. Most of these will live in China and South Asia.

That tally does not include the impacts of climate change. Global warming may already be affecting weather patterns, changing the time and place where rain and snow fall, say some experts.

Around 2.5 billion people today do not have access to decent sanitation, defying one of the targets of the UN's Millennium Development Goals.

Hydrologists say the crisis is rooted in excessive irrigation, leakage of urban water supplies, pollution of river water and unbridled extraction of water from nearly every type of source.

The Water Forum, running in Istanbul until Sunday, begins with a mini-summit of a small number of heads of state and government, invited by host Turkey. It concludes with a large ministerial gathering aimed at crafting guidelines for smarter management of water and resolution of water conflicts.

Outside the political dimension, the conference is also a gathering place for companies involving in the multi-billion water industry.

Between 92.4 billion and 148 billion dollars are needed annually to build and maintain water supply systems, sanitation and irrigation, according to a major document, the third World Water Development Report, that was issued in the runup to the Istanbul forum.

China and developed countries in Asia alone face financial needs of 38.2-51.4 billion dollars each year.

How this investment is mustered -- and the accountability of corporations in water, a key ingredient for life -- are among the big questions facing the conference.

Around 28,000 people are expected to attend the conference, the fifth in the series, according to an organisation official. "It breaks the record," she said.