Quenching the planet's growing thirst will be a gigantic task, with some experts warning that whole regions are in danger of drying up with catastrophic consequences for their impoverished populations.
Water was the focus of the Earth Summit on Wednesday, with developing countries pushing for a global target on sanitation to complement the Millennium Development Goal (MDG) of halving the proportion of people without access to clean drinking water by 2015.
South Africa is leading the charge to have a similar target hammered out for sanitation, but there is opposition on this score, notably from the United States and Australia.
"We have made great progress and the main opposition to a target on sanitation is now coming from the U.S. and Australia. It remains to be seen if they will come on line," South African Water Affairs and Forestry Minister Ronnie Kasrils told Reuters.
Among developed countries, Britain has come out very strongly in favor of a target.
"We firmly believe that a target is required to focus attention on this issue -- to halve by 2015 the proportion of people without access to sanitation," Britain's Secretary of the Environment Margaret Beckett said in a draft for the plenary session on water.
Host South Africa has blazed a path in water provision for others to follow, hooking up 10 million people to clean drinking water since the end of white minority rule in 1994.
Seven million still need water piped to them, but South Africa has already met the target of halving the proportion of its people without available and affordable drinking water.
Part of this has been accomplished by a "free water program" that provides most households in the country with 6,000 free liters per month.
This means affluent households with swimming pools and large gardens pay out, as they tend to use far more than their free allotment, while most of the poor who live in shacks get theirs free.
"The South African model is really exemplary," said Andras Szollosi-Nagy, a deputy assistant director general for UNESCO.
But on a global scale, the problem is daunting.
According to the U.N. 2002 Human Development Report, 1.1 billion people lacked access to safe drinking water in 2000, and 2.4 billion did not have adequate sanitation.
Experts say growing water scarcity is aggravated by desertification, deforestation and surging urban populations, especially in areas already suffering low rainfall such as parts of Africa.
The World Bank has said that to meet the MDG's development goals, around 300,000 people per day will have to be connected to water systems over the next decade. The estimated price tag is $25 billion a year.
Water consumption has outpaced swelling population growth, multiplying six-fold in the 20th century when the number of people on the planet tripled.
Agriculture is the biggest consumer, gulping close to 70 percent of all the water used by humanity.
Regions seen facing critical water shortages in coming years include North Africa and West Asia.
A World Bank report estimates that the Middle East and North Africa, with five percent of the world's population, have just one percent of the world's available freshwater resources.
The inequitable distribution of water among Middle Eastern states is an added source of tension in a region that is already one of the most unstable in the world.
Former South African President Nelson Mandela was to discuss water issues at the opening of the "Water Dome," which will host a series of events on water-related issues.