Only speculating but something tells me mineral water is often bottled while it's at still hot.
I didn't know what sous vide is. According to the wiki article, containers are either plastic or glass. It boggles the mind. Why would anyone cook in a plastic container
Sous vide is long waterbath at around 55 C or lower. Not a typical plastic safety issue temperature.
Cooking in plastic (or any "original package") has a food safety point in restaurants. Keeping it sealed until the outside is sterilized reduces possible contamination. Immersion also makes for easier and faster heating.
