By Alex Kirby
BBC News Online environment correspondent

If you want to induce mental meltdown, the statistics of the worsening global water crisis are a surefire winner.
Water-borne diseases already kill one child every eight seconds
Two-fifths of the world's people already face serious shortages, and water-borne diseases fill half its hospital beds.
People in rich countries use 10 times more water than those in poor ones.
The present is dire: the future looks so grim it must be entirely unmanageable.
Cut it how you will, the picture that emerges from today's data and tomorrow's forecasts is so complex and appalling it can leave you feeling powerless.
The world cannot increase its supply of fresh water: all it can do is change the way it uses it.
Its population is going to go on increasing for some time before there is any prospect it will stabilise.
Lion's share
And water-borne diseases already kill one child every eight seconds, as day follows day.
Water is not running out: it is simply that there are steadily more of us to share it.
Climate change will also have an effect on water - just what effect, though, nobody can really say.
Some regions will become drier, some wetter. Deserts may well spread and rivers shrink, but floods will also become more frequent.
Most of the world's water is already inaccessible, or comes in the form of storms and hurricanes to the wrong places at the wrong times.
But there is certainly room for better management of water in agriculture - which currently takes ups 70% of the water we use.
Drip irrigation, for example, minimises waste, as does low-pressure sprinklers and even simple earth walls to trap rainfall instead of letting it drain away too fast to be used.
Industry will usually make savings and cut costs wherever it can, and if it can spend less on water it will.
And us? One way to make consumers more responsible about water is to charge us for consuming it.
Running on empty
It works - up to a point. If water is expensive, those who can will economise on its use. But not everyone can.
Privatising the water supply in South Africa means many people now receive 6,000 litres a month free, then pay for whatever they use beyond that. A monthly 6,000 litres means 50 litres a day for a family of four.
Fifty litres is the recommended basic domestic water requirement, and by no means every South African family has only four members.
That is one reason why the anti-privatisation movement has been so strong in South Africa.
There is no one-size-fits-all prescription for the harsh business of bringing water demand into line with supply. Nor is there an off-the-peg way of engineering our way out of the crisis.
Agreeing to disagree
Desalination may play a part, but it is energy-hungry and leaves a brine mountain for disposal. Dams will impound more water, but can easily bring more problems in their train.
One of the disappointments of the World Water Forum in Japan in March 2002 was its focus on mega-engineering solutions like dams and pipelines, rather than using natural systems like forests and wetlands to conserve water.
There is some good news. Clean water and sanitation are getting to more and more people. But you may not have noticed, because the number of people benefiting was outstripped by the growth in human numbers.
Because the world's water suppy is finite, most of life's other necessities are finite as well. In China it takes 1,000 tonnes of water to grow one tonne of wheat.
If we do not learn to live within our aqueous means, we shall go hungry as well as thirsty.
A world where consumption was a means to survival, not an economic end in itself, would have enough water to go round. And polluted, inadequate water might kill its children a little more slowly.