160
L. Chai et al.
company or product, especially agricultural products, bottom-up can achieve a more
complete and detailed analysis due to its simple and intuitive characteristics.
According to different research objects and purposes, the types of water footprints
selected for accounting are also different. The Water Footprint Assessment Manual
provides seven types of water footprint [17], including product water footprint, boiler
water footprint, and corporate water footprint. Simultaneously, the Manual introduces
different calculation methods for different types of water footprints and accounting
purposes.
The bottom-up method is suitable for simple early analysis of the life cycle. Once
applied to the complex industry analysis, this method shows some shortcomings. First
of all, its data acquisition is very challenging. Taking industry as an example, industrial products’ production process involves multiple levels of raw material processing,
and the production of each level of raw material generates water loss, which is very
difficult for data statistics. Second, each industry, region, or country has tens of thousands of products produced. The calculation of the industry’s water footprint, region,
and country using the bottom-up method must include all products, which is very
difficult to operate [19].
2.3 Water Footprint Assessment Based on Top-Down Method
(IO Model)
Another way to calculate the water footprint is a top-down accounting method, in
which water is “embedded” in the value of each sector of the economy. With the
help of the IO model, construct a water resource IO table, conduct virtual water
volume research between departments and calculate the water footprint of various
products. This method was proposed by the scholar Leontief in the 1930s. The
method links the producers and consumers in the entire economic activity through
the links of production relations between departments. At the same time, by showing
the details of the flow of products between departments, it is possible to trace the
water consumption of products in the entire industrial chain [27]. In recent years of
research, IO methods have been widely used in the field of environmental footprint
assessment due to their simplicity and low data requirements.
3 Input–Output (IO) Model
3.1 The Emergence of IO Method
As early as the 1930s, Leontief, the American economist, has established IO analysis after accepting Walras’ general equilibrium theory and Marx’s reproduction
theory in theory [27, 30]. The IO analysis method mainly includes the IO table and
L. Chai et al.
company or product, especially agricultural products, bottom-up can achieve a more
complete and detailed analysis due to its simple and intuitive characteristics.
According to different research objects and purposes, the types of water footprints
selected for accounting are also different. The Water Footprint Assessment Manual
provides seven types of water footprint [17], including product water footprint, boiler
water footprint, and corporate water footprint. Simultaneously, the Manual introduces
different calculation methods for different types of water footprints and accounting
purposes.
The bottom-up method is suitable for simple early analysis of the life cycle. Once
applied to the complex industry analysis, this method shows some shortcomings. First
of all, its data acquisition is very challenging. Taking industry as an example, industrial products’ production process involves multiple levels of raw material processing,
and the production of each level of raw material generates water loss, which is very
difficult for data statistics. Second, each industry, region, or country has tens of thousands of products produced. The calculation of the industry’s water footprint, region,
and country using the bottom-up method must include all products, which is very
difficult to operate [19].
2.3 Water Footprint Assessment Based on Top-Down Method
(IO Model)
Another way to calculate the water footprint is a top-down accounting method, in
which water is “embedded” in the value of each sector of the economy. With the
help of the IO model, construct a water resource IO table, conduct virtual water
volume research between departments and calculate the water footprint of various
products. This method was proposed by the scholar Leontief in the 1930s. The
method links the producers and consumers in the entire economic activity through
the links of production relations between departments. At the same time, by showing
the details of the flow of products between departments, it is possible to trace the
water consumption of products in the entire industrial chain [27]. In recent years of
research, IO methods have been widely used in the field of environmental footprint
assessment due to their simplicity and low data requirements.
3 Input–Output (IO) Model
3.1 The Emergence of IO Method
As early as the 1930s, Leontief, the American economist, has established IO analysis after accepting Walras’ general equilibrium theory and Marx’s reproduction
theory in theory [27, 30]. The IO analysis method mainly includes the IO table and