Opened bottle
When you should stop drinking water
Many people fill reusable bottles with tap water.
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How long can you leave an opened water bottle standing before the water is no longer drinkable? This is something to keep in mind.
Water is one of the most important elixirs of human life. We should drink at least two liters of the clear liquid every day – especially on warm days. And so it happens that most people have opened water bottles lying around in various places – next to the bed, on the desk or in the car. Drinking a sip of water from the half-full bottle may seem harmless at first glance. But can water also go bad?
Mineral water quality has limits
Basically, mineral water is a strictly monitored foodstuff. It can always be drunk freshly opened – even if the bottle has been kept warm for a long time. However, mineral water also has a best-before date. This is legally prescribed in the Mineral and Table Water Ordinance. In glass bottles it is two years, in PET bottles it is about one year. If mineral water is stored in a cool, dark place – ideally in the refrigerator – it is usually drinkable long after the best-before date has passed.
But what about opened bottles? It is well known that water from an opened bottle tastes quite stale after a short time. This is because the chemical composition of the water changes as soon as oxygen gets into the bottle. As a result, the pH value of the water drops and a sour taste develops. This is not harmful, it just affects the taste.
However, from a health perspective, it is advisable to drink opened water bottles as quickly as possible. If the bottle is open, microorganisms can get into the bottle. If you drink directly from the bottle with your mouth, bacteria can also get into the bottle through saliva. Sharing bottles can therefore also be problematic.
Bacteria and germs in tap water
Many people rely on tap water for their fluid intake – after all, in Germany it is of high quality and also more environmentally friendly than bottled water. But what about its shelf life? In theory, water is considered non-perishable because it consists only of hydrogen and oxygen and does not contain any substances such as protein or sugar that could ferment.
However, when filled from the tap, the tap water comes into contact with environmental germs. According to the Federal Center for Nutrition (BzfE), however, this is not a problem. Factors that can increase the bacterial load, however, are light, heat and food (for example, dirty bottles or glasses).
The shelf life of tap water, just like mineral water, depends on correct storage. If you fill your water into clean containers and do not expose it to sunlight for long periods on warm days, you can drink it for a long time without worry. Reusable water bottles should be cleaned regularly in the dishwasher, and PET bottles should not be refilled more than once. In general, the health risk from germs or bacteria is relatively low for healthy people; the main thing that suffers is the taste of the water.