The world will grow more thirsty and unstable in the next generation as the number of people facing shortages of fresh water swells to 2.8 billion, according to a private study.

To reduce demand for drinking water in the future, the report from the Johns Hopkins University School of Public Health recommended that countries conserve water, pollute less, manage supply and demand of water better and slow population growth.It also said most countries need massive investments in sanitation and water supply infrastructure.

"A water-short world is an inherently unstable world," said the report released Wednesday. "To avoid catastrophe it is important to act now to slow the growth in demand for fresh water."

Now, nearly half a billion people don't have enough drinking water. That number is expected to increase to 2.8 billion people by 2025 - or 35 percent of the world's projected 8 billion people, the report said.

Today, 31 countries, mostly in Africa and the Near East, are facing water stress or water scarcity. By 2025, population pressure will push another 17 countries, including India, onto the list. China, with a projected 2025 population of 1.5 billion, will not be far behind, said the report.

A country faces water stress when annual fresh water supplies drop below 445,090 gallons per person. Water-scarce countries have annual fresh water supplies of less than 262,000 gallons per person.

Although much of the world is trying to meet a growing demand for fresh water, the situation is worst in developing countries where some 95 percent of the 80 million people added to the globe each year are born. In addition, the competition among industrial, urban and agricultural uses for water is mounting there, the report said.

Even in the United States, which has plenty of fresh water on a national basis, groundwater is being used at a rate 25 percent greater than its replenishment rate, said the report.

The report warned that regional conflicts over water could turn violent as shortages grow. And as people use more water, less is left for vital ecosystems on which humans and other species depend. Globally, over 20 percent of all freshwater fish species are endangered, vulnerable or have recently become extinct.