Water footprinting attempts to quantify the impact of human activities on freshwater-resources availability so as to provide a scientific basis for the sustainable utilization of freshwater resources.Whilst there is not yet unified method for water footprint assessment,the calculation metho.d for water footprint as proposed by the Water Footprint Network (WFN) is the most widely used in the world at present.Based on an analysis of the existing WFN calculation method,following the ISO 14046 Standard on water footprint,and the methodological framework of life cycle assessment (LCA),and focusing on the factors that determine freshwater-resources availability (viz.water quality,water quantity,and spatial distribution),we present,for the defined product life-cycle water availability footprint (WAF),an integrated calculation method that includes calculation of unit-process data,processing of background-process data,and aggregation of product life-cycle results.Application of the WAF calculation method to a case study of the textile production showed that this method:(1) can distinguish water pollution and water purification processes,and indicate the influence of regional water-resources scarcity on freshwater-resources availability via adopting a benchmark of water quality in definitions of water consumption and water pollution,and (2) can perform ISO-compliant modeling and calculation of life-cycle water footprint with support from existing LCA databases.However,the selection of the reference concentration of various pollutants in the calculation of unit-process data has unavoidable subjectivity and will directly affect the results of water footprint calculation,which needs further study.%水足迹方法试图量化评价人类活动对水资源可得性的影响,从而为水资源可持续利用提供科学的依据.水足迹的评价方法尚未统一,目前全球应用最为广泛的是WFN(water footprint network,水足迹协作网络)水足迹计算方法.基于LCA(life cycle assessment,生命周期评价)方法的基本框架,围绕水资源可得性的水量、水质和空间分布3个因素,在分析现有水足迹计算公式的基础上,指出了WFN水足迹计算方法的不足.根据国际水足迹标准(ISO 14046)的原则和要求,改进了WFN的水足迹计算公式,提出了产品生命周期WAF(water availability footprint,可得性水足迹)定义和评价方法,其中包括单元过程数据计算、背景过程数据处理和生命周期汇总.通过方法对比和案例研究得到:WAF方法统一了水消耗量与水污染量定义中的水质基准,可以明确区分水污染和水净化两类过程,还可以反映区域水资源稀缺程度的影响;采用WAF方法,在现有LCA数据库和软件的支持下可以更为规范地完成生命周期水足迹建模与计算但目前单元过程数据计算中各种污染物的基准浓度选取有不可避免的主观性,将直接影响到水足迹计算结果及其客观性,有待进一步研究.
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