TABLE 2.

Characterization of metrics relating to water use applied in the research literature concerning lower–environmental impact diets

Metric	Number of studies	Reliability1	Description
Blue water use	13	No	Volume of surface and groundwater consumed in the production of the different foods that make up the diet
Green water use	6	No	Volume of soil moisture from natural rainfall consumed in the production of the different foods that make up the diet
Virtual-water footprint	13	No	Sum of blue and green water consumption associated with the production of the different foods that make up the diet; can also include gray water, which is a theoretical volume of water required to dilute the load of pollutants emitted to freshwater to the natural background concentration or a selected water quality standard
Water-scarcity footprint	4	Yes	Each instance of water consumption is multiplied by a local Water Scarcity Index and subsequently summed across the life cycle of the different foods that make up the diet; an International Organization for Standardization (ISO14046:2014)–compliant metric

¹The ability to describe the relative level of environmental impact when applied in a life cycle context.