None of my skepticism should imply that I think everybody everywhere has all the clean, cheap water they need. Water, like all resources, is scarce, and I accept that scarcity can cause conflict. But before anyone starts frightening themselves about impending water wars, they might want to consider Barnaby's observation that in the last five decades there have been no "formal declarations of war over water.
The authors go on to argue that states tend to work out water shortages by importing food from water-rich nations.
I think it takes only one word to rebut that essay: Darfur. The Darfur conflict is all about water. The desert has migrated south 100 km in 40 years while the population has quadrupled. Pastorlists and farmers, both dependent on depleting water resources, began fighting to the death over what was left, and the government took the pastoralists' side. Without water scarcity, the Darfur genocide would not have happened. Period. Countries may be able to import food to counter water shortages, but poor farmers and pastoralists depend on it for their livelihoods, and they don't have the money to import new livelihoods. And this is not an isolated example. The entire Sahel, and much of East Africa, is facing the same issues.
Countries can import water to make up for shortages, but in poor countries, subsistence farmers and pastoralists depend on water for their livelihoods. Take that away, and disaster will strike. It's little exaggeration to say the entire Sahel is at risk of Darfurization.
Moreover, the fear of massive water loss could lead to problems like we've not known. India and Pakistan have reached water treaties in the past, yes, but today you've got over 1.5 billion people in the Subcontinent more or less entirely dependent on Himalayan meltwater. If climate change thins those glaciers and drastically reduces that flow, just as the population increases to well over 2 billion and adopts a more meat-heavy, water-intensive diet, never mind increased water usage by urban centers and industry... well, you can see where this could lead.