In a world running out of clean, accessible water, the question of who decides its allocation is crucial. Is access to water a human right or just a need? Is water a common good like air or a commodity like Coca-Cola? Who is being given the right or the power to turn on or off the tap - the people, governments or the invisible hand of the market? Who sets the price of water for a poor district in Manila or La Paz - the locally elected water board or the CEO of a big water corporation?

This is an important and controversial issue. A U.N. covenant would put nation-states on notice that it is their responsibility to provide clean water to their citizens. People have the right to demand safe, clean drinking water publicly delivered by their governments on a not-for-profit basis as a basic human right. The World Bank and the United Nations must make it a priority to build and support robust public institutions that guarantee water for all.

I have studied the history of for-profit water delivery in the Southern Hemisphere, which was imposed by the World Bank as a condition of funding, and the record is clear: Privatized water delivery results in high water rates, worker layoffs, decreased services, reduced water quality and water cutoffs to untold millions. Even the best private water companies must cut corners and use profits to pay dividends to their investors rather than investing in improved facilities.

Perhaps the greatest indictment of commercializing water delivery is the fact that, anticipating that the private sector would bring new investments for water services in poor countries, the lending banks and wealthy country donor agencies decreased their funding for water projects between 1998 and 2002 - a time when the need for services and aid in the global South exponentially grew.

This is not to say that there have not been public sector failures to provide clean water. There have. But governments are accountable to their citizens and can be changed.

Nor is this to suggest there is no place for the private sector in helping to find solutions to the global water crisis. Business has an important role in laying pipes, building infrastructure and cleaning and recycling dirty water. There is a huge role for the private sector in developing innovative technologies to save and clean water as well. I am particularly excited about innovations that apply biological science to technology - harnessing the power and processes of nature to transform toxic and industrial waste into clean water and even fuel - and the commitment of some businesses of reducing their water use.

However, the private sector must not be allowed to set water policy nor should the market determine who gets access to it. Corporate control of water would see water go to those who can buy it, not to those who need it. It would also encourage the plunder of water from nature, already a terrible problem. It would discourage conservation and source protection, arguably the first step in protecting the world's diminishing water supplies.

What we need now are guiding principles that set priorities for water. Water is a public trust that belongs to the Earth and all species. It is a basic human right. Yes, there is a commercial dimension to water. But the only possible path to a water secure future is based on the twin foundations of conservation and justice. All water use, public and private, must now serve these goals.