The substances in the watch list are to be selected from amongst those for which the information available indicates that they may pose a significant risk, at Union level, to or via the aquatic environment, but for which monitoring data are insufficient to come to a conclusion on the actual risk posed. Highly toxic substances, used in many Member States and discharged to the aquatic environment but not or rarely monitored, should be considered for inclusion in the watch list. That selection process should take into account information as itemised in points (a) to (e) of Article 8b(1) of Directive 2008/105/EC, giving particular consideration to emerging pollutants.

The monitoring of the substances in the watch list should generate high-quality data on their concentrations in the aquatic environment, fit for the purpose of supporting, in a separate review exercise according to Article 16(4) of Directive 2000/60/EC, the risk assessments that underpin the identification of priority substances. In that review, substances found to pose a significant risk should be considered for inclusion in the priority substances list. An environmental quality standard would then also be set which Member States would have to meet. The proposal of a substance for inclusion in the priority substances list would be subject to an impact assessment.

According to Article 8b(2) of Directive 2008/105/EC, the Commission is to update the watch list every two years. When updating the list, the Commission is to remove any substance for which a risk-based assessment as referred to in Article 16(2) of Directive 2000/60/EC can be concluded without additional monitoring data.

According to Article 8b(2) of Directive 2008/105/EC, the duration of a continuous watch list monitoring period for any individual substance shall not exceed four years. Therefore the watch-list monitoring obligation for the five substances or groups of substances that had been on the list since 2015, namely 17-alpha-ethinylestradiol (EE2), 17-beta-estradiol (E2) and estrone (E1), the group of macrolide antibiotics, methiocarb, and the group of neonicotinoids, ceased in 2019. The monitoring data obtained will be considered in the context of the prioritisation exercise referred to in Article 16(2) of Directive 2000/60/EC.

On the basis of the monitoring data obtained for the other three substances, namely metaflumizone, amoxicillin and ciprofloxacin, since 2018, the Commission concluded that insufficient high-quality monitoring data had been obtained, and that, therefore, those substances should remain on the watch list.

In accordance with Article 8b(1) of Directive 2008/105/EC, the Commission identified possible methods of analysis for the proposed substances. The method detection limit should be, for each substance, including each individual substance in a group, at least as low as the substance-specific predicted no-effect concentration in the relevant matrix.

Sulfamethoxazole and trimethoprim are commonly, but not always, used in combination because of their claimed synergistic effects; they can and should be analysed together even though they are not grouped together in the list. Venlafaxine and its metabolite are grouped because of their potentially additive effects; they can and should be analysed together. The azole substances are grouped because they have the same mode of action and could also have additive effects, despite their emissions coming from a range of sources and likely fluctuating over time; they can and should also be analysed together. The two fungicides, whose emissions are also likely to fluctuate, may but need not be analysed together.

The analytical methods specified in the watch list are not considered to entail excessive costs. If new information leads in the future to a decrease in the predicted no-effect concentration for specific substances, the maximum acceptable method detection limit may have to be lowered as long as those substances remain on the list.

For comparability, all substances should be monitored in whole water samples.

For reasons of legal clarity, the Annex to Implementing Decision (EU) 2018/840 should be replaced in its entirety. Implementing Decision (EU) 2018/840 should therefore be repealed.

The measures provided for in this Decision are in accordance with the opinion of the Committee established by Article 21(1) of Directive 2000/60/EC,