Michael McCarthy: World's most precious commodity is getting even scarcer

Ask yourself what the world's most precious commodity is, and you might say gold; you might say diamonds. You'd be wrong on both counts. The answer is water.

If by "most precious" we mean what's most desired by most people, nothing comes close to water - fresh, clean water, that is.

This basic truth has been hidden from us in the rich Western countries because we have long had such a plentiful supply. But much of the rest of the world has had no such luxury.

Across the globe, perhaps a third of all people suffer from "water stress". There are 1.1 billion people lacking access to clean water, 2.4 billion lacking access to improved sanitation, and half the world's hospital beds at any one time are thought to be occupied by people suffering from water-borne diseases. You think this is bad? It's going to get worse.

In 2003 a UN report predicted that by the middle of the century - in the worst case - 7 billion people in 60 countries could be faced with water scarcity, although if the right policies were followed this might be brought down to (merely) 2 billion, in 48 nations.

It doesn't take much to realise that with such a commodity in desperate demand, fights are going to break out.

The essence of the problem is that there is only so much water to go round, and as the world population mushrooms upwards, we are at last coming up against the limits of it.

You might not think so from a picture of the Earth, more than two-thirds of it water, making us the blue planet. But only about 2.5 per cent of it is freshwater, while the rest of it is salt. And of the freshwater, two-thirds is locked in glaciers and permanent snow cover. What is available, in lakes, rivers, aquifers (ground water) and rainfall runoff, is increasingly coming under pressure .

Population growth is the biggest pressure. Even though growth has slowed, the world population of 6.3 billion is likely to about 9.3 billion by 2050.

Demand comes not just from drinking, washing and human waste; the greatest calls come from industry in the developed world, and in the developing world, from agriculture. Irrigating crops in hot, dry countries accounts for 70 per cent of use. Pollution from industry, agriculture and human waste, adds fierce pressure. Finally, climate change will probably account for about a fifth of the increase in water scarcity. While rainfall is predicted to get heavier in winter in high latitudes, such as Britain and northern Europe, in many already-drought-prone countries and even some tropical regions it is predicted to fall.

Other pressures will also make themselves felt, such as the growing move of the world population into urban areas (which concentrate wastes) and the increasing privatisation of water resources.

But the combined effect of population growth, pollution and climate change will probably be enough to bring world water supplies to a critical point.

Although the issues of water and sanitation are now on the international agenda, thanks to being included in the Millennium Development Goals, the UN believes that the true scale of the potential world water crisis is still eluding world leaders. A nasty wake-up call may be on the way.