September 17, 2025, 4:12 am | Read time: 2 minutes
Bottled water, which should theoretically last indefinitely, has an expiration date. But why is that? The explanation lies in legal regulations, carbonation, and a bit of chemical reaction.
Legal Requirement for Labeling
Water bottles always have a best-before date, whether it’s still or sparkling water. But can it really go bad? “No,” answers Hannah Zeyßig to the question. The food expert from the Consumer Center NRW explains: The labeling is legally required because the EU mandates a best-before date. Many manufacturers opt for about two years. “This mainly concerns taste and perception, not safety,” Zeyßig explains.
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Storage Determines Quality
Unopened water is still drinkable after the date has passed, as long as it is stored in a cool, dry, and dark place. Under these conditions, microorganisms cannot become active. However, if the bottle is exposed to heat and sunlight, the taste can change. Water almost never becomes “bad” in a harmful sense, Zeyßig explains. “But it can become ‘undrinkable’ in terms of taste.”
Carbonation Protects Against Germs
Carbonation has a germ-inhibiting effect—that’s why sparkling water generally stays fresh longer than still water. Additionally, the materials of the bottles play a role. According to Zeyßig, glass bottles have an advantage because they reliably protect against flavor loss.
PET bottles, on the other hand, are less dense: Carbonation can escape, and at the same time, acetaldehyde can leach into the water when exposed to heat. Acetaldehyde is a colorless compound that can affect taste. However, the Consumer Center points out that it is not harmful to health.
The rule is: If you store purchased water properly, you can usually drink it well beyond the printed best-before date—even if the taste may change over time.
With material from dpa