In the keynote speech at London's annual City Food Lecture on Tuesday, Nestle CEO Paul Bulcke warned the world about the possible consequences of the global water shortage many experts believe will strike within the next several decades.

Noting that water scarcity could cut global cereal production by 30% by 2030, and that water needs already exceed supply, Bulcke called water scarcity the greatest threat to food security in the future. He urged global leaders to act soon to devise realistic solutions.

"It is only by working together with policymakers, civil society, agriculture and other stakeholders at local and international levels that we can develop effective, coherent and concrete action," Bulcke told the City Food Lecture attendees. "This is an issue that must be addressed urgently. I am convinced it can be solved. We should give water the right priority, the right value."

Nestle is the largest food company in the world by revenue, with 2012 sales of $86 billion. The company's position offers Bulcke an unusually large field of vision on the world's agricultural systems. The CEO has also been known for his (relatively) modest and media-shy personality.

Scientists have been saying for decades that the world's rivers, lakes and aquifers are going to have a hard time quenching the thirst (not to mention watering the crops and, yes, flushing the toilets) of 9 billion people. Major reports on the imminent water shortage, and the global humanitarian crises it might inspire, made headlines in 2006 and 2010. Like Bulcke's speech, these reports suggest that a serious water shortage could have dire consequences: famine, civil war, economic collapse.

True, Chicken Littles have been sounding alarms like this since Malthus published "An Essay on the Principle of Population," which says growing population rates will lead to poverty, in 1798. Technology has always managed to bypass perceived limits in the earth's ability to support humankind in the past. And technology, in the form of wastewater treatment, desalinization plants and new ways to conserve water, is likely to play a crucial role in mitigating a water shortage in the future.

Will life's fundamental building block become a major contributor to widespread disaster in the future? When the CEO of the world's largest food company is sounding the alarm, it may be time to listen.

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