With fresh water resources becoming scarcer worldwide due to population growth and climate change, a growing movement is working to make access to clean water a basic universal human right.

But it's a contentious issue, experts say. Especially difficult is how to safely mesh public-sector interests with public ownership of resources – and determine the legal and economic ramifications of enshrining the right to water by law.

"It's an issue that is snowballing," says Tobias Schmitz, a water-resources expert with Both Ends, a Dutch environmental and development organization. Some 30 countries have a constitutional or legal provision ensuring individuals' access to water, up from a handful a few years ago, he says.

"Everybody is grappling with the issue, knowing that we need to secure this right. But the question now is over the practical application of this right," Dr. Schmitz says.

Government officials and leaders of numerous nongovernmental organizations and companies working on the water issue are meeting this week in Istanbul as part of the World Water Forum, which takes place every three years in a bid to shape global water policy.

One of the thorniest issues governmental officials at the forum have struggled with has been this question of the right to water. A declaration to be signed by the ministers of some 120 countries attending the forum is expected to refer to access to water as a "basic need," rather than a right.

The United States – along with Canada, China, and several other nations – has so far refused to recognize the human right to water.

There are concerns among some countries – based on a misconception, experts say – that enshrining a universal right to water would force them to share their water resources with other nations.

China, for instance, is struggling just to provide its rising population with enough water. Rapid industrial growth and urbanization have taken a toll on the country's water supply, with underground sources quickly drying up.

Water usage in the country has quintupled over the past 50 years, forcing China to turn to massive and environmentally unfriendly engineering projects – such as diverting water from rivers – in order to meet demand.

An estimated 1 billion people worldwide lack access to safe drinking water and United Nations officials warn that the situation could get worse if current patterns of water use continue.

"Unless we change our water consumption behaviors, we will face a major crisis in fresh water," Koichiro Matsura, director-general of the UN Educational, Scientific and Cultural Organization (UNESCO), said at the forum, following the launch of a new UN report on the global water situation.

Experts in water issues say that providing citizens of a country with a legal right to what is deemed to be a minimally adequate amount of safe water would be an important way of mitigating the effect of any looming water crises.

"This is not a semantic issue. If we can determine that water is a right, it gives citizens a tool they can use against their governments," says Maude Barlow, a senior adviser on water issues to the president of the UN General Assembly.

"If you believe it is a human right, then you believe that you can't refuse to give it to someone because they can't afford it," she says.

In South Africa, for example, the 1996 Constitution guarantees access to "sufficient clean water" as a basic right, which has allowed individuals to take legal action when their water has been cut off.

A landmark 2006 ruling determined that inability to pay is not a good enough reason to cut someone's water off. The South African courts have also determined that every household must be provided with a minimum of 6,000 liters (1,585 gallons) of water per month, even if they can't afford it.

"You have pressures on both sides, between those who are pro-poor and those who are pro-development, but that has forced us to be innovative," says Rosalie Auriel Manning, a former board member of two large public water providers in Durban and Johannesburg. "It's a balancing act; you have to be clever."

Even the private sector, whose involvement in supplying water in certain parts of the world has proved to be both controversial and poorly received, is now embracing the concept of a human right to water.

"There is absolutely no conflict between the right to water and the private sector. Our industry supports the right to water," says Gerard Payen, president of AquaFed, an international federation of some 200 private water operators operating in over 30 countries.

"But we are practitioners, and as practitioners, we know that proclaiming the right to water is not enough," he adds. "Our job is to deliver water to people."

Delivering that water is certainly big business. Worldwide annual water-related investments are estimated at $400 billion to $500 billion.

Critics of the private sector say they are not opposed to its involvement in delivering water, as long as control of resources remains in public hands.

In some countries, like India, rights to water resources have been sold outright to private companies, which use them for their own needs or sell the water to individual users.

"There's a huge role for the private sector to help us secure our water future, but it has to be within this notion that water is a public trust," says Ms. Barlow, of the UN. "It's not the market that should decide who has access to water. It should be a public trust and a public right."