How much water does it take to produce a cup of tea? More than you might think - about 35 litres (8 gallons). That's because you need buckets of the stuff to grow the tea leaves in the first place. By the same logic, it takes about 1,450 litres to produce a kilogram of wheat. And a kilo of beef requires up to 15,000 litres, the amount necessary to grow the grain to feed the cow that ends up in your burger.

Today, on World Water Day, I'm reminded that the international food trade is essentially a form of water trade. If you live where water is scarce, it's more efficient to import sacks of corn than the millions of tonnes of water needed to produce it all yourself. So food becomes a kind of virtual water import.

This matters because water shortages and food prices are inextricably linked. For example, some agricultural economists say that as China's water tables continue to fall, depleted by drought and overuse, the country will inevitably import more grain, driving up global food prices. Higher food prices mean greater global food insecurity.

According to the U.N. Food and Agriculture Organisation (FAO), farming accounts for about 70 percent of global freshwater use, although the figure is more like 95 percent in some developing countries where farmers rely heavily on irrigation. "The planet is thirsty because it is hungry," FAO chief Jacques Diouf writes in today's Bangkok Post.

Just how thirsty are we? Across the globe, 1.1 billion people don't have access to clean drinking water, according to the United Nations. Some 2.6 billion lack adequate sanitation. That amounts to a worldwide water crisis that many aid agencies are calling a "silent emergency".

With global warming, a ballooning world population and rapid urbanisation, the stakes are getting higher. By 2025, experts say 3.4 billion people will be living in countries where water is scarce. Shortages will fuel conflicts and trigger mass migrations. Diseases will thrive and multiply amid poor sanitation.

According to a new World Vision report, a child dies of dehydration every seven minutes in the Asia Pacific region. Meanwhile, diarrheoa takes a far higher toll worldwide, killing about 5,000 children a day. Barbara Frost, of WaterAid UK, puts it this way in The Guardian: "The numbers of children that will die (today) because of inadequate water and sanitation would fill the equivalent of 20 jumbo jets."

What's to be done? I began this blog entry by talking about food production because many experts believe the agriculture sector, as the biggest user of water worldwide, should take the lead in tackling the crisis. That means finding ways to grow more food with less water while protecting rivers and basins.

But water management doesn't stop there, and a growing chorus of voices is calling on governments to link water scarcity to wider human development issues.

Writing in The New Zealand Herald today, UNICEF spokeswoman Georgina Newman urges the international community to get serious about meeting global Millennium Development Goals set by the United Nations to halve the number of people without safe drinking water and basic sanitation by 2015.

"If the international community can tackle issues like debt and poor trade treaties, why has it been so reticent in grappling with this far more fundamental roadblock to prosperity?" she asks. "At any one time, half the working population of Africa and Asia is unwell because of poor water quality. With ready access to water, poor countries would at least have a fighting chance to work themselves out of poverty."

Last November, the United Nations Development Programme put water at the heart of its Human Development Report 2006. Beyond scarcity: Power, poverty and the global water crisis contains a chapter on agriculture that shines the spotlight on poor farmers who make up the vast majority of the world's malnourished people.

"Intensifying competition for water is now one of the gravest threats to sustained human development," the report says. "Rising industrial demand, urbanisation, population growth and pollution are placing unprecedented stress on water systems - and on agriculture. As competition intensifies, social conflict over water is likely to increase. The danger is that those with the weakest human rights - small farmers and women producers in particular - will lose out."

The report recommends action to secure poor farmers' rights to water and give them better access to irrigation and "pro-poor" technology. It also suggests steps to help them adapt to climate change. Otherwise those who are most vulnerable to water scarcity will find their existence increasingly precarious.

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