The TFA (trifluoroacetic acid) chemical was detected in 24 out of 30 samples taken, particularly in Paris, according to the survey carried out by consumer rights organisation UFC-Que Choisir and the environmental group Future Generations.

TFA is a type of per- and polyfluoroalkyl substance (PFAS), often called forever chemicals because they do not degrade easily.

On top of that, in 20 out of 30 samples the concentrations of TFA exceeded European regulatory limits for 20 individual PFAS.

Under European Union rules, from 2026 all drinking water must not exceed 500 nanograms per litre for all PFAS.

NGOs are demanding that TFA be added to the list.

Of the 30 cities and towns where water has been analysed, the French capital's 10th district has the second highest concentration, at 6,200 nanograms per litre, behind Moussac in the south of France.

The town of Bruxerolles in western France came in third, at 2,600 nanograms per litre.

- 'No miracle solution' -

The groups lamented that in France, TFA is "rarely -- if ever -- sought by regional health agencies during drinking water controls".

"There is no miracle solution to offer consumers," Pauline Cervan, a toxicologist at Future Generations, told reporters on Thursday.

"Bottled water is also contaminated and filters are not effective."

In addition to TFA, the two groups analysed the presence of other forever chemicals in the water.

PFAS concentrations "remain in line with the standard chosen by France" where the limit is set at 100 nanograms/litre.

But this standard is "much less stringent than those of other countries" such as the United States and Denmark, the groups said, adding that French standards are "far too unprotective" and are not based on "any solid toxicological data."

If France were to apply the strictest standards and include TFA, 80 percent of the samples in the survey would be found to be non-compliant, said Olivier Andrault of UFC-Que Choisir.

"We therefore need to act," he added.

"At an individual level, it is impossible to escape PFAS," added Cervan. "So we need collective action by the public authorities."

A bill aimed at restricting the manufacture and sale of PFAS, which was adopted at first reading by lawmakers in the spring of 2024, is due to be put to the vote again next month.