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[1] https://ec.europa.eu/info/law/better-regulation/initiatives/ares-2017-5128184_en
[2] EC 2008: Water Note 7: Intercalibration: A common scale for Europe's waters http://ec.europa.eu/environment/water/participation/pdf/waternotes/water_note7_intercalibration.pdf
[3] Surface water ecological and chemical status; and groundwater chemical and quantitative status.
[4] CIS guidance no. 31: Ecological flows in the implementation of the Water Framework Directive. http://ec.europa.eu/environment/water/water-framework/facts_figures/guidance_docs_en.htm