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BPR Water Treatment Guidance: ECHA/EFSA Requirements for Drinking Water

  • 2 days ago
  • 5 min read

In August 2023, the European Chemicals Agency (ECHA) and the European Food Safety Authority (EFSA) jointly published a landmark guidance document on the impact of water treatment processes on residues of active substances in water abstracted for drinking water production (EFSA Journal, doi: 10.2903/j.efsa.2023.8194). For companies placing biocidal products on the EU market, this guidance is not merely a technical update. Rather, it represents a fundamental shift in how regulatory dossiers must be constructed. Its applicability requirements have been formally agreed and have become mandatory as of 1 April 2026.


What the Guidance Covers


The 2023 ECHA/EFSA guidance establishes a tiered framework to assess how water treatment processes (such as chlorination, ozonation, or UV treatment, etc.) transform residues of active substances into potentially hazardous compounds known as treatment transformation products (tTPs). This matters because some tTPs, such as nitrosamines, can be significantly more toxic than the parent active substance from which they derive.

The guidance applies to both plant protection products (PPPs) and biocidal products, but its implications are especially acute for the biocides sector, where products in areas such as drinking water treatment (Product Type 5), surface disinfection, and water used in food processing directly intersect with the water supply chain.


The BPR Regulatory Context


Under Regulation (EU) No 528/2012, no active substance may be approved, and no biocidal product may be authorized for market placement, without a rigorous demonstration that it does not pose unacceptable risks to human health, animals, or the environment. This explicitly includes risks arising via drinking water, either from direct use or from residues reaching water abstraction points.


The 2023 guidance fills a critical gap that previously existed in BPR compliance. While earlier frameworks addressed disinfection by-products in limited contexts, they did not systematically assess what happens when biocide residues or their environmental metabolites enter a water treatment facility and undergo further chemical transformation. That gap is now closed and its closure has direct consequences for both active substance approval applications and product authorisation dossiers.


When Does the Guidance Apply? The Agreed Applicability Rules


The question of when exactly this guidance becomes mandatory generated significant debate among EU Member States' Competent Authorities (CAs) for biocidal products, which was formally resolved at the 104th CA meeting in June 2024 (CA-June24-Doc.7.2).

The agreed conclusion is as follows:


The guidance will NOT apply to:

  • Active substance dossiers currently in the Review Programme. Given that the Review Programme has already been extended to December 2030, applying the new guidance to ongoing review submissions would induce delays to an already stretched schedule.


The guidance WILL apply to:

  • All other procedures both active substance approvals/renewals and biocidal product authorisations/renewals for which applications are submitted on or after 1 April 2026. Applications submitted before that date are not subject to the guidance.


This approach deliberately aligns with the applicability framework agreed for the ECHA guidance on risks to bees from biocide use, and with the general CA practice on implementing new guidance documents in the biocides area. It also mirrors, in broad terms, the schedule adopted by the PAFF Committee (Standing Committee on Plants, Animals, Food and Feed) for plant protection products though with one important difference: unlike in the PPP area, the CA did not restrict product authorisation applications to only those products whose active substance was already assessed under this guidance. The rationale is that in the biocides sector, active substance approvals do not typically cover all the uses relevant at the product authorisation stage, meaning the guidance retains independent relevance for product-level dossiers regardless of how the AS was evaluated.


It is also worth noting that applicants preparing submissions before 1 April 2026 are not prohibited from voluntarily applying the guidance. In fact, doing so proactively can help demonstrate compliance with the existing BPR requirement that residues must not cause unacceptable effects through drinking water.


The Four-Step Assessment Framework

The guidance introduces a structured, risk-proportionate methodology built around four sequential steps:


  • Step 1  Exposure at the abstraction point:

Using Predicted Environmental Concentrations (PEC), applicants must determine whether residue concentrations exceed 0.1 µg/L. If this threshold is breached, a full tTP formation assessment becomes mandatory.

  • Step 2  Identification of treatment transformation products:

Applicants must characterise which tTPs form during treatment processes. Any tTP detected above 0.075 µg/L triggers chemical identification and hazard characterisation.

  • Step 3  Toxicity assessment:

A tiered toxicological evaluation is applied to identified tTPs, starting with genotoxicity screening (Tier 1) and escalating to targeted experimental testing (Tier 3) where needed.

  • Step 4  Risk characterisation for the consumer: 

If risk is considered acceptable based on the above, appropriate risk management and monitoring measures are defined. If not, the use may be refused for specific applications or the authorisation rejected entirely.


What This Means for Industry


For companies holding or seeking BPR-compliant authorisations, the practical implications are significant. Dossiers submitted from 1 April 2026 onwards must incorporate this framework, meaning that toxicological and environmental fate data packages must now extend well beyond the active substance itself to encompass its transformation products under realistic drinking water treatment conditions.


Several structural challenges make this transition demanding. First, toxicological data on tTPs is often simply absent, forcing companies to rely on predictive in silico tools such as QSAR modelling and read-across approaches that regulators accept as a starting point but that frequently require subsequent experimental validation. Second, water treatment processes vary considerably across EU Member States, complicating the design of standardised simulation studies. Third, the costs and timelines involved in generating adequate tTP data can be prohibitive, particularly for SMEs.


Coordination between active substance manufacturers and downstream biocidal product formulators is also critical. Data on tTPs generated by AS manufacturers must flow effectively to formulators who bear responsibility for full product dossier compliance. Without early, structured communication across the value chain, gaps in data availability will translate directly into delays or refusals at the authorisation stage.


Proactive Compliance: Where to Start


Companies should treat the April 2026 deadline not as a future concern but as an immediate operational priority. The recommended starting points are:

  • Portfolio review: identify which active substances and product types have exposure pathways to drinking water abstraction areas.

  • PEC screening: conduct preliminary PEC calculations to determine which products trigger the full tTP assessment.

  • Supplier engagement: initiate dialogue with AS suppliers to understand what tTP data is already available and what studies remain outstanding.

  • Data gap analysis: map missing toxicological and analytical data against the tiered requirements of the guidance, and commission studies accordingly.


Conclusion


The 2023 ECHA/EFSA guidance on water treatment transformation products is a regulatory milestone that reshapes what compliance looks like for the biocides industry. It operationalises existing BPR obligations, that authorised products must not endanger health via drinking water, with a data-driven methodology that leaves little room for ambiguity. For companies placing biocidal products on the EU market, the question is no longer whether to engage with this framework, but how quickly and systematically they can build it into their regulatory strategy.


If you are a company looking for support in how to tackle this requirement, please don’t hesitate to contact our regulatory team


Author: Barbara DHOOP


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