A Model for the Assessment of the Water Footprint …
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will include all stages of water resource demand. In the calculation methodology,
this period is a calendar year (WFN) [35].
WF, in turn, for each of the processes, is composed according to its origin in three
variables: blue water footprint (WFblue), or freshwater consumed from a surface
or underground source extraction; green water footprint (WFgreen), or water from
precipitation and that is not converted into runoff and is absorbed by plants; and grey
water footprint (WFgrey), or volume of freshwater needed to assimilate the load
of pollutants by a receiving body, taking as a reference the environmental quality
standards, associating the limits established with good quality for the environment
and for people (see Fig. 4, Eq. 1).
The following point presents the model developed for the quantification of the
WF in the renewal of urban infrastructures related to the urban water cycle, and
not only the processes related to the amount of water necessary for the manufacture
of the material resources of construction and its implementation, but also, and in
a differentiated manner, the water consumption related to its use directly in the
area of study (green areas, irrigation, etc.), taking into account the incorporation
of infrastructure designed for water-sensitive areas. This means that the processes
taken into account range from the extraction of raw materials, the manufacture of
materials, transport, construction and the management of municipal services.
2.1 Model for Quantifying the Direct Water Footprint
2.1.1 Blue Water Footprint (WFblue)
The WFblue is defined by the WFN (see Fig. 4, Eq. 2) and considers the volume of
water that is incorporated and evaporates in a process. Most of the time the exact data
on the volume of water incorporated or evaporated is not available, so it is posed as
a water balance (see Fig. 4, Eq. 3).
The balance of the urban system is conditioned by the flows of inputs (rainfall and
irrigation) and outputs (filtration, evaporation and transpiration). Rainfall depends
on the local climate; i. e., it is conditioned by the geographical location of the system.
Irrigation, in turn, is defined by the water demand of the existing plants within the
system. The filtrations are due to the filtration capacity of the underlying soil and the
use of systems that allow rainwater to be drained off. Evaporation and transpiration
are determined by the presence of plants and the permeability of urban surfaces.
Finally, any volume of water that the system cannot assimilate in a given time is
transferred to the general sanitation network.
2.1.2 Grey Water Footprint (WFgrey)
In the WFN model, the WFgrey is presented as the volume of freshwater required
to assimilate the load of pollutants generated during an activity, based on the water
71
will include all stages of water resource demand. In the calculation methodology,
this period is a calendar year (WFN) [35].
WF, in turn, for each of the processes, is composed according to its origin in three
variables: blue water footprint (WFblue), or freshwater consumed from a surface
or underground source extraction; green water footprint (WFgreen), or water from
precipitation and that is not converted into runoff and is absorbed by plants; and grey
water footprint (WFgrey), or volume of freshwater needed to assimilate the load
of pollutants by a receiving body, taking as a reference the environmental quality
standards, associating the limits established with good quality for the environment
and for people (see Fig. 4, Eq. 1).
The following point presents the model developed for the quantification of the
WF in the renewal of urban infrastructures related to the urban water cycle, and
not only the processes related to the amount of water necessary for the manufacture
of the material resources of construction and its implementation, but also, and in
a differentiated manner, the water consumption related to its use directly in the
area of study (green areas, irrigation, etc.), taking into account the incorporation
of infrastructure designed for water-sensitive areas. This means that the processes
taken into account range from the extraction of raw materials, the manufacture of
materials, transport, construction and the management of municipal services.
2.1 Model for Quantifying the Direct Water Footprint
2.1.1 Blue Water Footprint (WFblue)
The WFblue is defined by the WFN (see Fig. 4, Eq. 2) and considers the volume of
water that is incorporated and evaporates in a process. Most of the time the exact data
on the volume of water incorporated or evaporated is not available, so it is posed as
a water balance (see Fig. 4, Eq. 3).
The balance of the urban system is conditioned by the flows of inputs (rainfall and
irrigation) and outputs (filtration, evaporation and transpiration). Rainfall depends
on the local climate; i. e., it is conditioned by the geographical location of the system.
Irrigation, in turn, is defined by the water demand of the existing plants within the
system. The filtrations are due to the filtration capacity of the underlying soil and the
use of systems that allow rainwater to be drained off. Evaporation and transpiration
are determined by the presence of plants and the permeability of urban surfaces.
Finally, any volume of water that the system cannot assimilate in a given time is
transferred to the general sanitation network.
2.1.2 Grey Water Footprint (WFgrey)
In the WFN model, the WFgrey is presented as the volume of freshwater required
to assimilate the load of pollutants generated during an activity, based on the water