Abstract Agricultural water productivity (WPAg) is considered by many as a valuable concept that links agricultural water use to the benefits it generates in terms of food (kg m −3 , kcal m −3 ) or income (US$ m −3 ). By extension, it can be hypothesized that WPAg is linked to rural poverty, and that its improvement would enable more people to benefit from a finite shared water resource. By reviewing case studies and analyses from four river basins and elsewhere, we find that WPAg and poverty are related, but that the strength of the relationship and its nature vary with scale. At a global scale, the link seems causal; improved water productivity will enable an expanding global population to feed itself from a finite water resource. At the local scale, improved water productivity is more often a consequence of other changes, such as crop productivity or value. At the intermediate scale of a basin or sub‐basin, WPAg represents the state of ecosystem services 1 “The benefits people obtain from ecosystems. These include provisioning services such as food and water; regulating services such as flood and disease control; cultural services such as spiritual, recreational, and cultural benefits; and supporting services such as nutrient cycling that maintain the conditions for life on Earth.” (Green Facts Glossary) http://www.greenfacts.org/glossary/def/ecosystem‐services.htm through which agriculture consumes water and from which groups of people generate food and income. In the absence of clear definitions of the links between water use by multiple actors and the outcomes produced, there is no evidence of causal linkages between agricultural water consumption and poverty. Awareness of WPAg of itself is unlikely to induce changes in agricultural practice that improve the livelihoods of water users, even though WPAg may increase as a result of general improvements in agricultural practice. Such linkages may, however, occur increasingly with water valuation in which users pay the real cost of the water that they use. Copyright © 2009 John Wiley & Sons, Ltd.