Exergy analysis (EA) has demonstrated to be useful in the assessment of the energy performance of technologies, including those regarding water management. In this paper, an EA-based index like the unit exergy cost (UEC) of different water-related technologies were obtained, from transport (pumping) to depuration and even brackish and seawater desalination. Those coefficients are important to quantify the additional energy consumption of present technologies with respect to the ideal ones, which correspond to the behaviour of a reversible process. Minimum UEC values were obtained in pumping techniques (1.5). Wastewater treatment plants (WWTP) ranged from 4 to 5, and commercial desalination varied from 5 (reverse osmosis) to 21 (multi-stage flash distillation). This affirms the fact that chemical-based water treatments are less efficient from the point of view of thermodynamics, however further improvements might be reached in those processes. Besides their embedded energy-efficiency information, the UEC values could be applied to assess water costs. For instance, the European Water Framework Directive (WFD) considers that environmental costs (those to restore water bodies up to an objective state) have also to be charged to water users. Consequently, the UEC values of water technologies together with energy prices could easily be used to estimate those environmental costs associated to physico-chemical degradation of water bodies.

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Purpose – The purpose of this paper is to check out the status of collected data in European water-related information tools, with the final aim of analyzing the cost to reach the good environmental status in European rivers, from recorded physical and chemical data, within the second law of thermodynamics. Design/methodology/approach – The study is especially focussed in an economical assessment to account for the environmental costs of water bodies according to the Water Framework Directive. The Catchments and Rivers Network System, the most important information tool in Europe nowadays, constitutes the support of this work. This study shows a methodology to estimate the cost to restore water bodies in energy terms with the help of an aggregated indicator, from physical and chemical characteristics of rivers. More over, energy results are converted later into an economic value. This work presents diverse case studies, starting from Garonne, Rhone, Rhine, Danube, Ebro and Seine rivers. Findings – Figures show that total environmental costs in rivers with higher flows are more important due to the more quantity of water to be restored. Making a contrast among years with different hydrological behavior, total environmental costs are higher in wet years due to the more availability of water to be supplied that consequently implies higher withdrawals. However, rivers with higher total environmental cost are not necessarily the most polluted ones. Regarding to the availability of data, although European monitoring and reporting is in progress, homogeneity of data and consensus in the management of basins are needed. Originality/value – Authors make an estimation of costs to reach the good status of European rivers. This work proposes the Exergy as an aggregate indicator to assess cost for water restoration in monetary values. This paper gives a reference of environmental cost as an important instrument to establish costs recovery prices, to be used in the management of water resources as a complement of other kind of indicators.

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