The study by Médecins en faveur de l’Environnement (MfE) and Pingwin Planet found one out of two brands of bottled water of 10 surveyed were contaminated, with two bottles extremely contaminated.
Swiss and international brands were tested but two glass bottles of Badoit, purchased in a Globus department store in Bern, had the worst score fro contaminants.
Produced by French food giant Danone, the Badoit was found to have 16,299 nanograms per litre of butylated hydroxytoluene, a food additive, more than three times the Swiss legal limit, according to the doctors group.
Strong levels of contamination of foreign substances were also noted in glass bottles of Valser and Henniez.
Lesser contamination was found in a glass bottle of Appenzell and Adelboner (plastic bottle), while slight contamination was found in plastic bottles of Appenzell and Aqua Classique.
M-Budget, Prix Garantie (Coop) and San Pellegrino were the only bottles waters found to be free of contaminants, according to the study reported in MfE’s online EcoScope publication.
The study also tested tap water from the city of Bern, which it said was free of contaminants and costs less than a third of a cent per litre, compared to 3.90 francs ($4.18) for the Badoit.
Tap water is purer and more environmental, the doctors said.
What is most surprising is that water in glass bottles seem to have the worst scores, Dr. Peter Kälin, president of MfE is quoted as saying by 20 MInutes newspaper.
One the explanations could be that glass bottles are recycled and residues can remain after they are cleaned for reuse.
The bottled water industry has contested the findings.
The Swiss association of mineral water and soft drinks said none of the brands analysed violate Swiss regulations.
Nestlé Waters Suisse, for its part, said it had conducted its own analysis of the products in question and its results “contradicted the principal results presented by MfE”.
The medical group’s findings, however, echo the results of similar research in the UK that found tap water is subjected to significantly more rigorous testing than bottled water.
In 2011, the Swiss office for public health studied 31 of the most popular bottled water brands in the country and concluded that none of them posed a health risk to the public.