Much of the technical vocabulary used by filtration specialists is regularly used in other industries or even in everyday language, which creates biases or distortions in the interpretation of statements between parties trying to understand each other. This was clearly seen in March 2025 during Senate sessions in France, which attempted to shed light on the practices of bottled water producers: the lack of understanding of the precise terms used by filtration professionals, who consciously allow themselves to use codified shortcuts, does not facilitate communication with uninformed interlocutors. The message is further muddied when the commercial arguments of certain filter manufacturers or distributors highlight performance or characteristics that are unrelated to any methodological or normative reference or even simple explanation.

At IFTS, the Institute for Filtration and Separation Techniques, we felt it was important to make a useful contribution by providing technical insights into the topics discussed during these Senate examinations (membrane pore size and particle filtration efficiency), avoiding oversimplification while striving to remain understandable to as many people as possible.

This document presents the methods used to characterize microfiltration membranes, adopting a normative and scientific style. It details, in particular, the techniques used to measure pore size distribution, as well as performance (efficiency) tests based on particle retention.

This document indirectly highlights the need to fill certain gaps in European standards (EN standards) in the field of membrane filtration processes, particularly with regards to the vocabulary used and testing methods. Referencing these international European methods would be a valuable aid in avoiding any possible contradictory interpretations in the European regulations imposed in the field of water treatment.