When considering the supply of water in any area, one must first
construct a regional water budget. A generalized water budget for
any region includes evaporation from water bodies, formation of
clouds and the precipitation of this moisture. Evapotranspiration
from terrestrial surfaces, surface runoff and infiltration to charge
groundwater supplies are also included. These structural relations
between precipitation, evapotranspiration and infiltration provide
the basis for calculating regional water supply footprints in our
research. The application of this simple conceptual model as
demonstrated later in the paper allows for elaborating the research
question for our proposed WSF concept: “How big is the catchment
area required for a sustainablewater supply taking the regional and
local water cycle and the supply-demand balance into account?”
This measure can again be expressed in m2 per year and, given this
spatial dimension, is consistent with the broader EF concept.