The world's top bottled water seller Nestle Waters used "food safety" treatments that infringe French law, the company told AFP Monday.
It said it had passed some waters, such as Perrier and Vittel, through ultraviolet light and active carbon filters "to guarantee food safety", confirming an initial report from business daily Les Echos.
Nestle said it "lost track of the importance of conforming to regulations" but that all the brands concerned now fulfil French requirements.
It said it told the French authorities in 2021.
Nestle did not immediately make clear when it stopped treating water sold under the Perrier, Vittel, Hepar and Contrex brands.
French law bans any disinfectant treatment of mineral waters, which are supposed to be safe to drink when they emerge from their sources.
Tap water, by contrast, is disinfected before being classed as drinkable.
Nestle said there had been "changes in the environment around its sources, which can sometimes make it difficult to maintain stability of vital characteristics" in the water -- namely the absence of pollution and mineral composition.
Since stopping the treatments, Nestle has paused production at some wells in the Vosges department of eastern France due to their "sensitivity to climate hazards", forcing it to slash production of Hepar and Contrex.