Does it actually get bad? Why mineral water has an expiry date

One hopes for a refreshing and tingling sip of water – and instead gets stale slop.

The bad taste of stagnant water raises the question of whether the whole thing could be a health hazard.

To get straight to the biggest concern: It’s not dangerous to drink stagnant water. The reason for this is that bottled water usually does not drain.

Stagnant water changes chemically

If a bottle has been opened several times or a glass of water has been left standing for a long time, only the chemical composition changes: the water absorbs carbon dioxide from the air and some of the liquid becomes carbonic acid, causing the pH value of the water to drop.

This means that the drink tastes a bit sour – and the palate immediately recognizes that it is stale water.

Apart from the taste buds, however, no region of the body is affected. As a rule, the consumption of stagnant water is therefore not harmful to health.

Provide water with best-before dates

Although drinking water that has been open for a long time is actually harmless, there is an expiry date on water bottles. However, this is only an expiration date.

As the Table Water Ordinance states, manufacturers are obliged to indicate such a date.

However, even after this period has expired, you can drink the water without hesitation, says the German mineral water information center: “The carbonic acid conserves the mineral water and makes it last almost indefinitely,” says their website.

Be careful with water from plastic bottles?

For a long time it was considered unhealthy to drink water from plastic bottles. The reason for this: The packaging is said to release hormone-like chemicals into the water, researchers assumed that long-term consequences cannot be ruled out.

But this assumption is now considered outdated in science, as Dr. Frank Welle from the Fraunhofer Institute for Process Engineering and Packaging reported to Stiftung Warentest.

According to the expert, PET contains neither hormones nor hormone-like substances such as bisphenol A: “So far, no specific substance has been detected that has a hormonal effect,” says Welle.

“Neither the Federal Institute for Risk Assessment nor the monitoring authorities were able to confirm such results,” he adds.

However, the situation is different for other substances that could migrate into natural mineral water.

One such example is acetaldehyde.

“It is produced during the production of PET, i.e. polyethylene terephthalate. Acetaldehyde is harmless to health. However, if it migrates into the water in too large quantities, it can taste chemically sweet. Great heat, for example in overheated cars, accelerates the process. Other substances such as ethylene glycol, terephthalic acid or antimony can also migrate into the mineral water – in harmless quantities,” says Welle.

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Federal Ministry of Justice and Consumer Protection (1984): Ordinance on natural mineral water, spring water and table water, retrieved on May 12, 2022:

Information center German mineral water: All information about mineral water, retrieved on May 12, 2022:

D. Schymanski (2018): Analysis of microplastics in food and cosmetics, retrieved on May 12, 2022: -and-cosmetics

Stiftung Warentest: mineral water in the test; Interview: Hormones in PET bottles?, retrieved on May 12, 2022:

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