Secretary-General Ban Ki-moon is warning that by 2030 nearly half the world's population could be facing a scarcity of water, with demand outstripping supply by 40 percent.
Ban said one in three people already live in a country with moderate to high water stress. He spoke Friday at a U.N. event marking the opening of the International Year of Water Cooperation 2013 and the 20th anniversary of the proclamation of World Water Day.
He said "competition is growing among farmers and herders; industry and agriculture; town and country; upstream and downstream; and across borders."
With a growing global population and climate change, he said international cooperation is essential to protect water resources.
"Let us use it more intelligently and waste less so all get a fair share," Ban said.