Wendy Barnaby is hasty in her conclusion that water shortages can and will be resolved through international trade and economic development (see Nature 458, 282–283; 2009). She predicts that nations will be able to adapt to water shortages as they develop, by switching to industries other than agriculture and by importing their food from elsewhere. But this assumes both that developing nations will be able to afford food and that food itself is not also a limited resource being threatened by global warming.

Barnaby's implication that poorer nations will become wealthier in the coming decades is at odds with the global reality of an increasing gap between rich and poor (Report on the World Social Situation United Nations Department of Economic and Social Affairs; 2005) and with the repeated failure of such development plans (J. Ferguson Global Shadows Duke Univ. Press; 2006). Evidence of the causal relationship between inequality and the failure of economic development (W. Easterly J. Dev. Econ. 84, 755–776; 2007) makes it ever harder to imagine that development is going to become successful in the near future.

In addition to the increasing inequality of nations, the gap between rich and poor citizens is widening in countries around the world. This means that the belief in cooperation as the “dominant response to shared water resources” needs to be further questioned by analysing how water is distributed within nations. For instance, 'water management devices' (meters) are being installed in poor people's homes in Cape Town, South Africa; in Chile, water privatization has allowed mining companies to monopolize scarce water supplies, forcing people to abandon their home towns as water dries up.

Access to water is already a serious issue for people in many parts of the world and, given recent United Nations estimates, the situation is not likely to improve. In light of this, we believe that embracing international trade and development as easy or inevitable solutions is naive. The reality of global inequality, power and poverty — and their impact on access to water — must be taken seriously in any plan for addressing future water shortages.

See also: The potential for water conflict is on the increase Water is a source of cooperation rather than war