Do you know that? An open bottle of mineral water suddenly tastes stale after a while. This inevitably raises the question of whether mineral water can go bad?

Mineral water from PET bottles lose their taste more quickly

It’s not that easy. The best-before date is prescribed by law and is not an official expiry date. According to the German mineral water information center, “mineral water can still be enjoyed without hesitation even after the deadline has expired.”

Water in plastic bottles has a shorter expiry date than water in glass bottles. There is a specific reason for this: water from plastic bottles loses its taste faster because oxygen can penetrate the PET bottle better than glass.

It is also rumored that hormone-like chemicals could escape into the water if the PET bottle were to heat up. A study by the University of Frankfurt am Main examined this suspicion. The biologists Jörg Oehlmann and Martin Wagner reported that twelve of the 20 types of mineral water tested contained a hormone similar to female estrogen.

Why does my mineral water taste stale?

The biologists also report that the estrogenic load in PET bottles is twice as high as in glass bottles. One reason for this could be the plasticizers contained in the plastic. According to the Frankfurter Allgemeine Zeitung, there are indications that this could gradually detach itself from the plastic and migrate into the water. It has not yet been confirmed whether this can also lead to health problems, but it is at least suspected.

Nevertheless, opened bottles should be consumed within a few days. Because microorganisms such as bacteria can get into the open bottle – and multiply there quickly. This happens quickly, especially in the summer when it is bright and very warm, according to the researchers at the Mercy Medical Center. Therefore, it is also recommended to store opened bottles in cool places.