UNITED NATIONS (Reuters) - The world needs to act urgently to avoid a global water crisis due to increased population, rising living standards, dietary changes and more biofuels production, the United Nations warned on Thursday.

By 2030, nearly half of the world's people will be living in areas of acute water shortage, said a report jointly produced by more than two dozen U.N. bodies and issued ahead of a major conference on water to be held in Istanbul next week.

"Despite the vital importance of water to all aspects of human life, the sector has been plagued by a chronic lack of political support, poor governance and underinvestment."

The growth rate means demand for fresh water is increasing by 64 billion cubic meters a year, the report said. Authors told a news conference that most of North Africa and the Middle East had already reached the limits of their water resources.

"The impact could be large for some countries, including China and India, and for some regions of large countries, such as the United States," it said. "There could also be significant implications for water resources, with possible feedback into global grain markets."

Government and business leaders needed to act now to boost investment in water infrastructure, it said, adding, "Unsustainable management and inequitable access to water resources cannot continue."