Regulatory Convergence between the Drinking Water Directive (EU 2020/2184) and the Biocidal Products Regulation (BPR)

1. Institutional framework and protection objectives

The sanitary safety of drinking water in the EU is primarily based on an increasing synergy between two legislative pillars: Directive (EU) 2020/2184 (Drinking Water Directive), which constitutes a revision of the pre-existing Directive 98/83/EC, and Regulation (EU) No 528/2012 (BPR). Although their scopes differ, they converge towards a common goal: the protection of human health. While the BPR governs the placing on the marketing and use of biocidal products (including drinking water treatment products), the Drinking Water Directive defines quality requirements at the tap through a risk management approach.

In this interaction, four categories of actors are involved:

• Competent authorities and EU agencies: ECHA, EFSA, the European Commission and national authorities, responsible for governance and scientific arbitration.

• Industry and applicants: manufacturers of active substances (AS), formulators of biocidal products, and economic operators responsible for the compliance of files.

• Technical operators and suppliers: water suppliers and operators in the food sector ensuring treatment and distribution.

• Professionals and the general public: building professionals and end consumers, benefiting from safe water.

2. The “dual key” principle

The implementation of biocidal solutions in emissions integrated into the water cycle requires two-step validation validation to ensure consumer safety.

1. The first key, defined by the Biocidal Products Regulation (BPR), corresponds to the Authorization for Placing on the Market (AMM in French). This is the fundamental prerequisite for a biocidal product to be marketed. The BPR evaluates and validates the effectiveness of a disinfectant for a specific use and examines the intrinsic risks associated with this product, both for human health and the environment.

2. The second key is determined by the Drinking Water Directive, which focuses on compliance of water at the tap. This step represents the validation of the performance of the biocidal product under real usage conditions. The objective is to ensure that an authorized biocide never leads to exceeding the water quality standards set.

3. Technical requirements and evolution of chemical quality

The guarantee of safe drinking water relies on the strict application of quantified health thresholds, on a rigorous framework for substances used in treatment to prevent any alteration of quality, and the implementation of a dynamic monitoring system to track the evolution of knowledge concerning new pollutants, as presented in various sections of Directive 2020/2184.

Defined under article 12, the use of chemical treatment agents and filtration media is subject to four imperatives:

1. Human health: no direct or indirect compromise of health protection. 

2. Organoleptic quality: maintenance the colour, odour and taste of water. 

3. Microbiological stability: no unintended microbial proliferation. 

4. Minimal contamination: strict limitation of residues to the level necessary for the intended use. 

Contamination by by-products must be kept as low as possible. To address emerging pollutants, the directive introduces, in Article 13, an obligation for Member States to monitor water for chemical parameters and substances or compounds of concern identified in a watchlist (Watch List), such as PFAS, endocrine disruptors, or microplastics, whose parametric values will be specified in delegated acts by the European Commission.

The parametric values used to assess water quality are defined by minimum requirements to be met, presented in Annex I of the directive, and cover microbiological, chemical and indicator parameters.

4. Risk-based approach: from source to tap 

The legislation requires a systemic analysis covering the entire supply chain (Article 7):

• Extraction (Art. 8): assessment of environmental risks in abstraction areas.

• Treatment & distribution (Art. 9): management of risks related to water treatment processes and the network. 

• Private installations (Art. 10): monitoring of the internal distribution up to the tap.

5. Joint ECHA/EFSA Guidance (2023)

The 2023 joint ECHA/EFSA Guidance aims to harmonize the assessment of active substance (AS) residues and their transformation products in drinking water. 

Starting from 1 April 2026, this guidance became mandatory for all new submissions. It specifically includes consideration of environmental transformation products (eTPs), formed in the environment before entering the plant, and treatment transformation products (tTPs), formed during drinking water treatment processes through methods such as chlorination or ozonation. Some of these products, like nitrosamines, may be more toxic than the parent active substance.

This regulatory evolution could have a significant impact on biocide manufacturers, potentially affecting them upstream of the active substance manufacturers, resulting in longer approval timelines for dossiers.

6. Risk assessment methodology and critical alerts

The assessment of residues and transformation products from the use of biocides (and plant protection products) is divided into four successive steps:

• Step 1: exposure assessment at the abstraction point via PEC (Predicted Environmental Concentrations). If PEC > 0.1 µg/L, a full assessment of tTP formation is triggered. 

• Step 2: detection of transformation products (tTPs) from water treatment process. A concentration > 0.075 µg/L triggers chemical identification and hazard assessment. 

• Step 3: toxicity assessment of formed products according to a tiered approach, from potential for genotoxicity (Tier 1) to targeted testing (Tier 3). 

• Step 4: risk characterization of the risk to the consumer. If exposure is acceptable, management and monitoring measures can be defined.

7. Strategic impacts and industrial challenges 

With the implementation of this regulatory framework, the biocides industry faces several structural obstacles that complicate its development and adaptation to regulatory requirements, with major strategic implications for the entire value chain.

On a scientific and public health front, the lack of toxicological data concerning tTPs is a central challenge. In many cases, no experimental data is available regarding their genotoxicity or general toxicity. This gap forces industry players to rely on predictive approaches such as in silico models (QSAR, read-across). Although these tools provide an initial assessment, they generate significant uncertainties and frequently require subsequent experimental validation, impacting costs and timelines. This situation creates a strategic risk because the lack of robust data can delay or jeopardize authorization procedures.

On the technical side, the complexity of evaluations is exacerbated by the lack of standardization of drinking water treatment processes at the European level. While the final water quality is regulated, treatment methods vary significantly depending on local contexts. Therefore, manufacturers must design specific experimental protocols, incorporating numerous parameters (raw water quality, pH, temperature, natural organic matter), making studies difficult to replicate and harmonize. The identification of tTPs is itself a major analytical challenge, requiring advanced technologies and non-targeted approaches capable of detecting compounds at extremely low concentrations.

From an economic perspective, the costs associated with treatment simulation studies are considerable, making these analyses difficult for many companies, especially smaller ones, to access. Moreover, the time required to complete these studies is often incompatible with strict regulatory deadlines, creating tensions between legal requirements and operational capabilities within the industry.

Coordination between the different actors in the value chain, especially between active substance (AS) manufacturers and biocide formulators, is also a critical issue. It is imperative to establish a smooth and efficient data-sharing process to ensure product compliance and safety throughout their life cycle. This cooperation would allow for better anticipation of risks and faster response to regulatory requirements.

Finally, the regulatory consequences in case of uncertainty or identified risk are particularly structuring. In the absence of effective risk mitigation measures (RMM), non-compliance due to the presence of concerning tTPs can lead to the refusal of market authorization. Additionally, even if an active substance is approved, the identification of a toxic tTP in the formulated product may lead to rejection for a specific use. This situation places companies at high commercial risk and forces them to integrate tTP-related challenges early in their development, formulation, and marketing strategies.

8. Strategic recommendations for operators 

To ensure safe market access, operators must adopt a rigorous and proactive strategy:

1. Review of product portfolio and associated active substances. To identify products that may pose a problem and implement appropriate solutions.

2. In parallel, a thorough analysis of PECs must be conducted to verify if the critical threshold of 0.1 µg/L is exceeded. This step is crucial to ensure that products meet safety standards and do not present any risks to human health or the environment.

3. Evaluate specific uses of products, particularly those that pose a risk to abstraction areas.

4. Operators should engage in proactive and collaborative dialogue with active substance suppliers to improve availability of data on tTPs.

Conclusion 

• According to the BPR, the conditions for granting authorization include ensuring that the biocidal product itself, or its residues, does not have an unacceptable immediate or delayed effect on human health and the environment, including vulnerable groups, or on animal health, directly or via drinking water, food, animal feed, air, or other indirect effects.

• The publication of the 2023 Joint Guidance ECHA/EFSA does fill a gap in recommendations for assessing effects via drinking water. However, the deadline of April 1, 2026, represents a breaking point: action must be taken now to anticipate the delays linked to technical studies.

Authors : Floriane Demailly & Loris Mistrulli