A new methodological approach to improve the monitoring of tap water

The monitoring of drinking water normally relies on what are known as "targeted" methods, in which the analysis focuses on a predefined list of chemical compounds. Only the compounds actually screened for are therefore likely to be detected and quantified. 

However, new techniques now enable the non-targeted analysis of chemical compounds in water. Combining chromatography with high-resolution mass spectrometry, they can obtain a chemical signature of the compounds present in a sample, from a single analysis. The molecules are then identified by comparing the chemical signatures obtained with those available in databases. 

Nevertheless, these methods are not universal: some compounds may not be detected despite being present in the sample, or may only be detected with a low level of confidence that does not allow them to be identified with certainty.

First application of the non-targeted approach to drinking water on a national scale

Can a non-targeted approach help to identify emerging compounds in drinking water more effectively? To answer this question, ANSES's Laboratory for Hydrology, based in Nancy, tested this approach for the first time during its most recent campaign to measure the prevalence of emerging chemical compounds, carried out from 2023–2025. The laboratory regularly conducts such campaigns to detect and measure compounds that are not normally included in the regulatory monitoring of water. 

The non-targeted method tested was based on liquid chromatography coupled with high-resolution mass spectrometry. It was applied to the analysis of 206 samples of raw water and 202 samples of treated water, collected throughout France, including from the overseas territories. Several quality control measures were put in place to ensure the reliability of the results.

Several compounds identified for the first time

During the initial phase of this study, 93 compounds were identified in raw water and 79 in treated water (i.e. water ready for consumption). 

While most of these molecules had already been detected during earlier exploratory campaigns, several compounds not previously monitored in drinking water were identified for the first time: they included pesticide metabolites, residues of pharmaceutical compounds, industrial compounds and substances used in daily life. 

At this stage, the purpose of the test was solely to verify its ability to detect emerging compounds not included on the usual lists, without measuring their concentrations. The possible risks to health were therefore not assessed. 

Moreover, some of the chemical signatures could not be identified with sufficient certainty. A new phase of analysis of the results has begun in order to conduct more in-depth investigations.

Guiding future national campaigns

This proof of concept confirms the relevance of non-targeted analysis in national campaigns on emerging compounds, as a supplement to targeted approaches. 

The results will help guide the laboratory’s future work by focusing on some of the compounds detected in order to measure their concentrations. 

More broadly, non-targeted approaches offer great promise for better characterising all the types of chemical exposure, as part of the "One Health" concept. ANSES is therefore working to deploy the methodological frameworks needed to incorporate these approaches into its research, assessment and expert appraisal activities, going beyond their application to water alone.