More than two-thirds of the Earth's surface area is covered by water. But the world is heading for a water crisis in the 21st century set to dwarf all droughts of history, according to a major investigation.
In 25 years the world will be 20 per cent short of water even if every country implements the most efficient conservation programmes imaginable, the projection shows.
Ismail Serageldin, chairman of the World Commission on Water, blames the crisis on a rising population, ever-increasing demand and worsening pollution of existing supplies.
"Water is life," said Mr Serageldin. "Shortage of fresh water is looming as the most serious obstacle to food security, poverty reduction and protection of the environment. It's going to be one of the major problems of the 21st century."
The World Commission, international experts funded by the World Bank and the United Nations, will this week call for a global initiative to tackle the problem. "Even if we do everything we can to make irrigated agriculture more water efficient, humanity will still need at least 17 per cent more fresh water to meet all its food needs than is currently available," Mr Serageldin said. "If we follow business-as-usual, all water sectors will need 56 per cent more."
Cities will compete with agricultural communities for water and countries will fight for access to supplies, Mr Serageldin predicts.
Water shortages in parts of the world are already devastating people's lives, health and happiness, the World Commission reports.
An estimated 1.4 billion people live without clean drinking water, a further 2.3 billion lack adequate sanitation and 7 million die every year from water-borne diseases.
Half the planet's rivers and lakes are seriously polluted and many of the world's biggest rivers - such as the Yangtse in China - fail to flow to the sea year round because of water extraction.
The World Commission estimates that nearly 450 million people in 29 countries already face water shortages. Within 50 years, it predicts this will be 2.5 billion people in 55 countries. A major problem is that most of the world's growing population is concentrated in areas where fresh water is in short supply. Two-thirds of the people alive today live in areas that receive only a quarter of the world's annual rainfall.
The experts say the entire Mediterranean region - North Africa, India, parts of China, most of sub-Saharan Africa and large regions of North and South America - will face severe shortages.
Half the freshwater lakes in Europe - one of the most important sources of drinking water - are severely affected by pollution, and other sources of clean water are being contaminated by human activity.
Over the past 30 years, improvements in agriculture have doubled production of grain. "The increase came mostly on irrigated lands, which comprise less than a fifth of all cropped area but produce some 45 per cent of the world's food," the World Commission says. "As a result, the number of people eating less than 2,100 calories per day, as the standard index of nutrition, has fallen by three-quarters.
"But irrigated agriculture will have to provide 70 per cent of the increased food needed for an additional 3 billion people expected by 2025." Mr Serageldin said this was the heart of the problem. The typical efficiency of water use - the amount of irrigation going directly into growing crops - is about 45 per cent, which needs to rise to at least 70 per cent in most regions to keep the water gap to a minimum.
But, the World Commission reports: "Depending on rain-fed agriculture would cause massive environmental damage; more land would have to be cleared, forests would be lost, habitats would be destroyed and biodiversity would be threatened.
"Every hectare of irrigated land represents 2.5 hectares of pasture or forest that need not be developed for agriculture."
With urban populations expected to triple in 30 years, supplies for cities will dwindle. Aquifers supplying Beijing, Buenos Aires, Dhaka, Lima and Mexico City will vanish, leaving an estimated 150 million urbanites to hunt for fresh supplies.Reuse content