HESS Opinions: How should a future water census address consumptive use? (And where can we substitute withdrawal data while we wait?)

Abstract

Despite the centrality of the water balance equation to hydrology and water resources, in 2018 we still lack adequate empirical observations of consumptive use of water by humans and their economy. It is therefore worth considering what we can do with the withdrawal-based water use data we already possess, and what future water census measurements would be required to more accurately quantify consumptive use for the most common mesoscale use cases. The limitations of the currently applied simple net consumptive use (SNCU) assumptions are discussed for several common use cases. Fortunately, several applied water management, economics, and policy questions can be sufficiently addressed using currently available withdrawal numbers in place of water consumption numbers. This discussion clarifies the broad requirements for an improved "stock and flow" census-scale data model for consumptive water use. While we are waiting for the eventual arrival of a more sophisticated water census, the withdrawal data we already possess are sufficient for some of our most important scientific and applied purposes.