2015 年 11 巻 1 号 p. 22-31
Objective. A Water Footprint (WF) can be expressed as the potential impacts calculated based on the consumed amount of water or the quality of degraded water through the entire life cycle of products/services/organizations. The principles, requirements and guidelines of water footprinting have been established as an international standard. According to the draft of the international standard, various elementary flows such as the quantity of water used, type of water resource, type of water appropriation, quality of water, geographical location of water withdrawal and return flows are required to be considered in a water inventory. This study distinguishes the type of water resource and the form of water use in a water inventory database. However, most existing water footprint inventory databases have not dealt with the quality of water. The purpose of this study was to develop a water footprint inventory database that will make it possible to evaluate water degradation.
Results and Discussion. The amounts of Nitrogen (N) and Phosphorus (P) in discharged water were selected as inventory items representing water degradation. The amounts of these substances in discharged water were converted to potential impacts on the environment. The volume of dilution water needed to bring the levels of degradation to the accepted quality level in the environmental regulations was calculated for representing the potential impacts. Input-output analysis was adopted to obtain water intensity for 403 industrial sectors from cradle to gate. The volume of dilution water required in secondary industries was estimated to be higher than those in other industries. For primary industries, the study revealed that agricultural crops required large amount of dilution water because of the larger indirect demand of dilution water in secondary industries in the upstream of the supply chain. The inventory data for tertiary industries were influenced by the degree of demand in the sewage sector. Comparing the intensities of consumed water and dilution water in each industry, dilution water was generally more dominant than consumed water in secondary industries. On the other hand, consumed water was more dominant in primary industries due to the large demand of water input and the relationship of them in tertiary industries was depending on the relations to secondary industries in the upstream of the supply chain.
Conclusions. The output of this study, a database of water inventories, includes achieves to include the aspects of water degradation in water footprinting by representing potential impacts from N and P emission in discharged water. This database enables practitioners to carry out water footprint analyses following the requirements in the ISO standard draft. While the database in this study was developed based on the average data for the whole Japanese activities, geographical location will also be an important aspect for assessing potential impacts of water use as mentioned in the ISO standard draft of water footprinting. The distinction of geographical location of inventory and other emission substances in addition to N and P need to be considered in the future studies.