Dr Glen Daigger, senior vice-president of the International Water Association, said there was growing evidence that spending on clean water and sanitation was the single greatest contribution to reducing disease and death. The UN has identified dams for hydropower and irrigation as leading drivers of sustainable economic growth in developing countries. "Water and sanitation is clearly a better investment than medical intervention, but it's not sexy," added Daigger.

    Last year the World Bank called for investment in water infrastructure to more than double from $80bn to $180bn over the next 20-25 years to cope with population growth and climate change, which are expected to leave about 4 billion people living in "water stress" areas - deemed to have insufficient water to meet daily needs. Conditions would be particularly severe in Africa, the Middle East and South Asia, said the bank. Water pollution and the threat to coastal areas of erosion, sea level rise and storm surges are also growing concerns.

    However, experts meeting at the IWA conference of 2,700 water professionals in Vienna suggested the true scale of the problem could be much higher.

    Prof Pavel Kabat, one of the lead authors of the water chapter in last year's report by the UN's Intergovernmental Panel on Climate Change, said investment needed to rise to 1.5% of GDP for 20 years, just to cope with existing population demand and climate variability. Africa, the region with the greatest lack of infrastructure, would have to spend its entire forecast GDP growth for more than half a century even to reach relatively modest levels of water storage and supply; and even Europe would have to triple spending.

    Failure to invest would mean "we'd have more recurrent floods and droughts because our systems are not able to take the magnitude and frequency of water we're witnessing," he said. It would also undermine other development spending in poorer nations, said Kabat, citing the example of Kenya, where he said two extreme years of wet and dry in the 1990s destroyed 40% of the country's wealth.

    "If these things are not in place we can keep on building schools but we're not doing the right thing," he added.

    Among the proposals to reduce costs, water users would have to accept different grades of water, including a lower grade in gardens and toilets, said Professor Alexander Zehnder, of the Alberta Water Research Institute, Canada. "Why are we spending a lot of money to clean the water and then we piss in it?"

    Earlier this year the American Society of Civil Engineers said the US needed to spend $1.6tn over five years to repair all its crumbling infrastructure, and gave the worst assessment of all to the water sector. Federal funds for drinking water were less than 10% of what was needed.

    In the UK the Institution of Civil Engineers said that despite significant investment since water privatisation in 1989 many mains pipes were extremely old and in poor condition, and under-investment in new reservoirs had led to "insufficient winter reserve storage to sustain supplies in extreme conditions".

    Last year's floods in the UK exposed fears about the safety of a reservoir dam in Yorkshire, leading to 100 homes being evacuated. Yesterday the Chartered Institution of Water and Environmental Management warned that floods were having "devastating" health, social and economic consequences.

    "Impacts can range from immediate death, injury and harm from contaminated water, through to lasting psychological consequences caused by damaged homes, loss of personal possessions and financial worries," said the London-based institution.

Brown Danube

    The Danube

    Despite its role in European history, the Danube has been neglected. A report out today says that, despite improving, nearly half its 1,771-mile length fails to meet European Union standards.

    Many cities in former Soviet countries that line its banks do not treat waste water and flush the sewage of millions of residents straight into Europe's second-longest river and down to the Black Sea.

    The International Commission for the Protection of the Danube River, which has published the report, says more than 200 schemes costing €4.5bn (£3.6bn) are needed just to treat waste water. Drinking water supply projects costing about half that much again are also required, said Philip Weller, the commission's executive secretary.

    But the affected countries are all in eastern Europe and do not have the money, he said. "The hope is some of those investments will come from the European Union; some will have to come direct from the countries."

    Africa

    Water stress is defined as having less than 1,000 cubic meters of water a year per person. By this definition up to 2.1 million people already have too little, and population growth and more variable rainfall threaten to make this much worse.

    The problems are acute in south-east Asia and Africa, but Africa is least able to cope. Average US storage capability is 6,000 cubic metres; in China it is less than half of that and in many countries in Africa it is minuscule. To bring the region up to South Africa's level of nearly 750 cubic metres would need all the estimated 5%-7% rise in national income every year for up to 80 years.

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