The effects of climate change, which is altering the pattern of rainfall and water evaporation around the world, are already apparent in some parts of the country. East Anglia, including Cambridge, has been officially classified a "semi-arid" zone, receiving an average of 60cm (24in) of rain annually - less than many parts of Italy. "It may seem damp if you live in Cambridge, but the actual precipitation is really quite small," said Professor George Solt, a visiting professor at University College London. "In the summer there is a `rain deficit' which is only made up by downfalls the rest of the time."
Rivers are particularly affected, with many coming close to drying up during summer, then overflowing in spring. In the past few years that has led to floods across the country around Easter - followed by dry, hot summers.
"Certainly in England and Wales we are presently looking at warmer, drier summers," said Robert Flavin at the Institute of Hydrology, Britain's premier resource on historic groundwater and river levels. "Though in Scotland, everything points to warmer and wetter summers." The past 25 years have all been drier and hotter than the historic average, he said.
At the Climatic Research Unit at the University of East Anglia, Professor Philip Jones noted: "There's going to be more demand for water, particularly in the south-east of Britain, because we use more both domestically and in farming when we have warmer summers."
Similar pressures caused by global warming are already being felt in the United States and Canada. At the weekend, scientists at a conference in Toronto were told that the five "Great Lakes" on the US/ Canadian border are at their lowest level this century.
The cause is thought to be increased evaporation caused by warmer air. With a surface area of 94,250 square miles, the Lakes are the largest bodies of fresh water in the world.
Scientists at the conference said that such low levels were not predicted to recur for another 50 years. But increased demand for fresh water, and particularly for bottled water or bulk volumes taken directly from the Lakes' groundwater feeds, is also believed to be affecting levels and quality.
Fresh water is forecast to be a growing bone of contention between and even within nations in the next century. Two weeks ago a report by the United Nations Environment Programme declared that by 2025 two-thirds of the world's population would live in countries suffering "water stress". Presently, one-third of the world's 6 billion population live in such conditions.
But those pressures will be felt in the developed world, as well as in developing countries. In Canada, the province of Ontario has banned bulk exports of water from the Great Lakes; even so, mineral water companies extract billions of litres from groundwater sources annually without being charged. That is likely to change.
Global warming means that glaciers in the Alps are retreating. Winter snow tends to melt immediately in the thaw, rather than being locked into glacial ice - and causes enormous variations in river levels between spring and summer.
However the most likely area for conflicts to arise over water is the Middle East, particularly between Israel and Jordan. The water supply from the River Jordan is maintained only by agreements between countries. Some analysts have even predicted the next world war might break out in a dispute over water from the Jordan.Reuse content