Water footprints: Path to enlightenment, or false trail?

•Water footprints are compared to carbon footprints.•The concept of water footprints as a policy tool is evaluated.•Procedures for computing water footprints are critiqued.•Uncertainties in the partition between “green” and “blue” water are identified.•The limited usefulness of absolute (as distinct from relative) water footprints is discussed.

Virtual water and water footprints have gained recognition as indicators to guide action on issues related to water scarcity. I argue that water footprints are fundamentally different from carbon footprints, as local reductions in carbon emissions have global benefits, while global attempts to reduce water footprints will have neither necessary beneficial impacts in areas of local water scarcity, nor global impacts on atmospheric water content. In addition, water footprints have little or no meaning for purposes of setting policy regarding national water use or international trade. Furthermore, the calculation procedures adopted in most estimates of water footprints are flawed. Finally, I suggest that water footprints are incorrectly assessed on an absolute, rather than a relative basis. Water analysts are fortunate to have hydrology, a science with agreed procedures and standards, to use in describing the physical impacts of interventions in the hydrologic cycle. Generalised water footprints are neither accurate nor helpful indicators for gaining a better understanding of water resource management.