Cholera may return to London, the mass migration of Africans could cause civil unrest in Europe and China's economy could crash by 2015 as the supply of fresh water becomes critical to the global economy. That was the bleak assessment yesterday by forecasters from some of the world's leading corporate users of fresh water, 200 of the largest food, oil, water and chemical companies.

Analysts working for Shell, Coca-Cola, Procter & Gamble, Cargill and other companies which depend heavily on secure water supplies, yesterday suggested the next 20 years would be critical as countries became richer, making heavier demands on scarce water supplies.

In three future scenarios, the businesses foresee growing civil unrest, boom and bust economic cycles in Asia and mass migrations to Europe. But they also say scarcity will encourage the development of new water-saving technologies and better management of water by business.

The study of future water availability, which the corporations have taken three years to compile, suggests water conflicts are likely to become common in many countries, according to the World Business Council on Sustainable Development, which brought the industrial groups together.

Lloyd Timberlake, spokesman for the council, said: "The growing demand for water in China can potentially lead to over-exploitation and a decline in availability for domestic, agricultural, industry and energy production use. This inevitably leads to loss of production, both industrial and agricultural, and can also affect public health - all of which in turn will ultimately lead to an economic downturn. The question is how can business address these challenges and still make a profit."

The corporations were yesterday joined by the conservation group WWF and the International Water Management Institute, the world's leading body on fresh water management, which said water scarcity was increasing faster than expected. In China, authorities had begun trucking in water to millions of people after wells and rivers ran dry in the east of the country.

"Globally, water usage has increased by six times in the past 100 years and will double again by 2050, driven mainly by irrigation and demands of agriculture. Some countries have already run out of water to produce their own food. Without improvements ... the consequences will be even more widespread water scarcity and rapidly increasing water prices," said Frank Rijsberman, director of the institute.

The institute, funded by government research organisations, will report next week that a third of the world's population, more than 2 billion people, is living in places where water is overused - leading to falling underground water levels and drying rivers - or cannot be accessed.

Mr Rijsberman said rising living standards in India and China could lead to increased demand for better food, which would in turn need more water to produce. He expected the price of water to increase everywhere to meet an expected 50% increase in the amount of food the world will need in the next 20 years.

According to the institute's assessment, Egypt imports more than half of its food because it does not have enough water to grow it domestically and Australia is faced with water scarcity in the Murray-Darling Basin as a result of diverting large quantities of water for use in agriculture. The Aral Sea in central Asia is another example of massive diversion of water for agriculture in the Soviet era causing widespread water scarcity, and one of the world's worst environmental disasters.

Researchers say it is possible to reduce water scarcity, feed people and address poverty, but the key trade-off is with the environment. "People and their governments will face some tough decisions on how to allocate and manage water," says the institute's report.

In a further paper, WWF said yesterday that water crises, long seen as a problem of only the poorest, are affecting the wealthiest nations. "In Europe, countries along the Atlantic are suffering recurring droughts, while water-intensive tourism and irrigated agriculture are endangering water resources in the Mediterranean. In Australia, salinity is a major threat to a large proportion of its key agricultural areas", said Jamie Pittock, director of WWF's freshwater programme.

In the United States, Mr Pittock said, large areas are already using substantially more water than can be naturally replenished. "This situation will only be exacerbated as climate change is predicted to bring lower rainfall, increased evaporation and changed patterns of snow melting."

Three visions of the future

1. Misery and shortages in the megacities and drought in Africa

By 2010, 22 megacities with populations larger than 10 million face major water and sewerage problems. The situation is gravest in China, where 550 of the country's 600 largest cities are running short. Growing demand for water by industry leads to serious over-exploitaion with less and less water available for consumers and farmers. This leads to a fall in Chinese food production, which in turn leads to more imports and impacts on other countries. Friction and unrest grow worldwide as the middle classes struggle to pay bills. Businesses are exposed to charges of moral culpability and litigation over water use. Waves of immigrants flood in to Europe from increasingly drought-torn Africa

2. China leads recycling rush as world moves to a new hydro economy

By 2010, the water shortage in many developing countries is recognised as one of the most serious political and social issues of the time. Lack of water is stopping development and in many countries the rural poor suffer as their water and other needs take second place to those of swelling cities and industry. Local government worldwide is increasingly distrusted over water allocation, and historical divides between rich and poor are exacerbated by water shortages. However, by 2025 a worldwide hydro economy is developing, led by China. Vast new investments are made in recycling water and the cost of desalination is greatly reduced. Innovative small-scale water treatment processes become the norm

3. Water is the means of social control as floods and disease devastate world

Water becomes a key symbol of protest around the world and is seen as the most serious social and political issue of the generation. By 2015, multinational companies are accused regularly of taking too much water in developing countries, cholera breaks out in London, and governments start to use water as a form of social control, subsidising some sectors and rationing it to others. Great floods follow each other in quick succession. Deforestation leads to massive mudslides in Asia and increasing flooding affects Europe, damaging industry. A second New Orleans flood destroys the city again. Global focus grows on the "export" of water via crops such as wheat or fruit