Will the world run out of water? To put it another way, as the planet's population swells, its temperature increases and its rivers and basins shrink, will we have enough water to produce all the food we drink?

That's not a typo. I say "drink" because, as I noted last week on World Water Day, food production and water use are inextricably linked. On average, it takes a litre of water (about a quart) to produce every calorie we eat. A typical vegetarian requires 2,000 litres a day for his or her meals. A meat-eater needs a whopping 5 tonnes.

"Imagine a canal 10 metres deep, 100 metres wide (330 feet), and 7.1 million kilometres (about 5 miles) long - long enough to encircle the globe 180 times. That is the amount of water it takes each year to produce food for today's 6.5 billion people. Add 2-3 billion people and accommodate their changing diets from cereals to more meat and vegetables and that could add another 5 million kilometres to the channel of water needed to feed the world's people."

This comes from a new report entitled Water for food, Water for life, the result of research from more than 700 global water specialists. Billed as an exhaustive assessment of water management in agriculture, the study answers the question of whether there'll be enough water to meet our growing food requirements like this: "Yes, if..."

"If a lot of things are done differently..." explained the report's editor, David Molden, at an event in London organised by the Overseas Development Institute. He went on to describe a world already at water tipping-point. "We've reached the situation where some very important limits for water are reached, or even breached."

The study highlights a number of disturbing trends - not least the fact that 850 million people remain malnourished worldwide. Pollution is on the rise and rivers are drying up due to greater agricultural production and water consumption. Pastoralists are putting grazing lands under increasing pressure. And overexploitation is fast depleting groundwater levels in densely populated areas of northern Africa, northern China, India and Mexico due to overexploitation.

It doesn't end there. According to Molden, there's no water left for development in some of the world's biggest closed river basins, including the Yellow River, the Nile, the Colorado, the Murray-Darling and the Indus. Meanwhile, with fisheries at their limit, aquaculture will become more prevalent, further straining freshwater resources.

So what could we do differently?

"Basically we have to change our way of thinking about water and food," Molden said, outlining eight broad policy actions. These include concrete steps to help farmers get "more crop per drop" and technological solutions to water harvesting, irrigation and water conservation.

They also encourage us to see the savannah lands of the semi-arid tropics as parts of the globe where we're likely to make the biggest gains in raising water productivity and reducing poverty.

Returning to the original question, the report concludes: "The hope lies in closing the gap in agricultural productivity in many parts of the world - often today no greater than that on the fields of the Roman Empire - and in realising the unexplored potential that lies in better water management along with nonmiraculous changes in policy and production techniques.

"The world has enough freshwater to produce food for all its people over the next half century. But world leaders must take action now - before the opportunities to do so are lost."

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