The European Union’s Recast Drinking Water Directive (2020/2184) entered into force on 12 January 2021 and requires the Commission to adopt, within three years, a methodology for measuring microplastics in drinking water. To support this mandate, the Joint Research Centre (JRC) conducted a comprehensive review of the scientific literature and its own experience to assess the nature, distribution and quantities of microplastics in potable water and to evaluate analytical techniques that could be incorporated into a monitoring framework. The review identified three principal categories of instrumentation: fluorescence microscopy, optical micro‑spectroscopy (Raman and infrared) and thermo‑analytical methods such as pyrolysis and thermal‑extraction‑and‑desorption coupled with gas chromatography/mass spectrometry (GC/MS). Each technique offers distinct advantages and constraints. Fluorescence microscopy provides rapid screening and can detect particles down to a few micrometres, but it cannot identify polymer type. Raman and infrared spectroscopy can determine polymer composition and detect particles as small as 1 µm, yet they are limited by the need for clear optical access and can be time‑consuming for large sample sets. Thermo‑analytical methods yield mass‑based measurements and can quantify polymer types, but they require complete combustion or extraction of the sample and are less suitable for particle counting. The review also collated performance data from inter‑laboratory comparisons, including a JRC/BAM study on polyethylene terephthalate (PET) in water, a Southern California Coastal Water Research Project (SCCWRP) comparison, and a German Centre for Water Technology assessment. These exercises demonstrated that the number concentrations of microplastics and fibres in drinking water span five orders of magnitude, typically ranging from 0.01 to 100 particles per litre. European studies most often report concentrations below 1 particle per litre, while global data show higher values in some regions. The review highlighted that the current analytical landscape lacks a single, harmonised method that simultaneously delivers high sensitivity, particle‑size resolution, polymer identification and throughput suitable for routine monitoring. Two partially relevant standards exist: ASTM D8332‑20, which outlines sampling practices, and ISO 24187, which sets principles for sampling, treatment and detection, but neither fully addresses the specific needs of drinking‑water monitoring.

The project was carried out by a multidisciplinary team of JRC scientists—Susanne Belz, Claudia Cella, Otmar Geiss, Douglas Gilliland, Rita La Spina, Dora Mehn and Birgit Sokull‑Kluettgen—who coordinated literature searches, data synthesis and inter‑laboratory validation. Collaboration extended beyond the JRC to national and international partners. The German Federal Institute for Materials Research and Testing (BAM) contributed to the PET inter‑laboratory study, while the Southern California Coastal Water Research Project provided comparative data from the United States. The German Centre for Water Technology supplied additional validation data and insights into practical sampling protocols. These partnerships enabled cross‑validation of methods and facilitated the exchange of best practices. The initiative was funded by the European Commission under the Recast Drinking Water Directive, reflecting the EU’s commitment to ensuring safe drinking water through evidence‑based monitoring. The outcomes of the review form the technical foundation for the Commission’s forthcoming methodology, guiding the selection of measurement metrics—mass or number—particle descriptors such as size, shape and polymer type, and the choice of analytical techniques that balance sensitivity, throughput and cost.