“You indicate that the scarcity-weighted water footprint hasn’t been widely accepted. Is there any specific reason or is it just that it hasn’t caught on yet?”

First, a quick review of the logic of the scarcity-weighted water footprint. The water footprint of a food, consumer item, individual, or company is the sum of all the water that it took to make that food / item (or to make all the items consumed by that individual or sold by that company). The problem with a simple water footprint is that it doesn’t distinguish between water use in water-abundant places, where water use is not really a problem, and water use in water-scarce places, where that water use is contributing to groundwater depletion, river drying, and water shortages. Enter the scarcity-weighted footprint, which weights water use more heavily if it takes places in water-scarce locations.

There’s been an extensive back-and-forth between the Water Footprint Network (WFN) folks (who popularized the concept of the water footprint and don’t like scarcity weighting) and the Life Cycle Assessment (LCA) folks (who have extensive experience with weighting in environmental metrics other than water and want to apply it to water as well). At its most basic, this is a culture clash. This paper (from the WFN perspective) and response (from the LCA perspective) offer a good overview of the discussion.

One underlying issue is the question of whether – despite the very different water realities of different locations – water should be considered a global resource after all, in light of the fact that food is a global resource. If you think of the water problem as “how do we grow enough food to feed the world with the water that is available to us globally?” then the goal would be to minimize the (non-weighted) water footprint of our food; in that view, scarcity-weighting obscures the goal of minimizing global water use. However, this perspective does ignore local effects: the impacts of water use for food production very much depend on where and how that food is grown. There is no simple answer here.