The head of the UN environment programme, Dr Klaus Topfer, says he thinks a war triggered by water scarcity is very likely.

Dr Topfer, a German who earlier served as his country's environment minister, makes the prediction in an interview with the journal Environmental Science and Technology (EST).

EST is published by the American Chemical Society, which with more than 155,000 members claims to be the world's largest scientific society.

Dr Topfer says he is "completely convinced" that there will be a conflict over natural resources, with water the likeliest of the possible causes.

"Everybody knows that we have an increase in population, but we do not have a corresponding increase in drinking water, so the result ... is conflict."

Avoiding waste

Dr Topfer proposes monitoring worldwide reserves of drinking water, and establishing agreements for the use of water, including underground supplies.

He argues as well for "economic instruments to stimulate the use of new technologies" to promote water conservation.

And with an eye to the dramatic global population growth he expects, Klaus Topfer calls for a revolution in the efficiency with which we use water.

He wants the new, more efficient technologies to be made available "on preferential terms" to developing countries.

Pollution is reducing the inadequate water that is available

On the brink of the new millennium, the world has no more fresh water than it did 2,000 years ago, when the population was less than 3% of its present size.

That finite resource is in fact becoming smaller, as fresh water is increasingly unuseable because of pollution.

Thirty one countries, most of them in Africa and the Middle East, are now suffering water stress or scarcity.

By 2025, the total affected will probably number 48 countries.

One in four goes without

They will account for 35% of the expected global population by then.

And countries like China and Pakistan will be close to joining the list.

The human cost of water scarcity today is immense.

About 1.4 billion people, a quarter of the world's population, do not have access to clean, safe water. More than 2 billion people have no proper sanitation.

Access to safe water pays huge dividends

Every hour more than 600 people die because their water supplies are contaminated, inadequate, or non-existent.

And the health of many of those who survive is often permanently damaged.

Yet the benefits of tackling the problem are similarly immense.

A review of nearly 150 studies shows that providing clean water and sanitation meant infant and child deaths fell by an average of 55%.

Some countries registered even greater declines.

In Costa Rica, for example, there were in the 1970s 68 deaths per 1,000 live births.

In the 1980s this figure had been reduced to 20 per 1,000.