Opinion of Advocate General Kokott delivered on 28 March 2019.#Proceedings brought by Wasserleitungsverband Nördliches Burgenland and Others.#Request for a preliminary ruling from the Verwaltungsgericht Wien.#Reference for a preliminary ruling — Environment — Directive 91/676/EEC — Protection of waters against pollution caused by nitrates from agricultural sources — Objective of reducing pollution — Waters affected by pollution — Maximum nitrate level of 50 mg/l — Action programmes adopted by the Member States — Rights of individuals to have such a programme amended — Locus standi before the national authorities and courts.#Case C-197/18.