Why not boil water twice in the kettle?

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Can you reboil leftover water in the kettle? Opinions are divided on the question. Many fear residue in the water. Is the fear well-founded?

Boiling water in the kettle twice? For many, this is out of the question. For fear of deposits that allegedly endanger health, they tip away the residual water and prefer to boil fresh water. According to a survey of 500 Germans conducted by the Fresenius Test Institute in 2017, 53 percent of respondents prefer to refill the kettle. The other 47 percent have no problem with the residual water.

The experts from the Fresenius Institute say that one in two of those who throw away old water are afraid of germs in the residual water. Every third person is afraid of dissolved pollutants. Limescale deposits and an unappetizing taste are also cited as reasons for preferring to use new water for boiling.

Is the fear justified?
Probably not. “The fear of stale boiling water is a relic from the days of immersion heaters and tea kettles,” Gisbert Lemke of the testing laboratory SGS Institut Fresenius informs in a press release. “Modern kitchen appliances are tested for product safety. Consumers should look for the GS seal when buying a kettle.”

If the water stands for a while, harmful residues such as bisphenol A or nickel accumulate, according to the fear of 36 percent of respondents. However, this is mostly unfounded, Lemke says. “In fact, household appliances that we test in our laboratories for the GS seal rarely show problematic contamination.”

Bacteria
Many tip away the old water because they are afraid of germs and bacteria. According to 54 percent of those surveyed, these could spread in the residual water over time. This is true in principle, because germs are everywhere in the environment. So they can also get into the water. However, this does not usually have any health consequences. In most cases, boiling the water again kills any pathogens that may be present. However, if you only heat the residual water and do not bring it to the boil, you should actually prefer to use fresh, cold water from the tap.

Taste
Limescale deposits in the residual water are the reason for 59 percent to prefer to use fresh water for boiling. And 31 percent think that boiled water doesn’t taste as good to them. According to Gisbert Lemke, however, there is no scientific evidence for this. “Some tea experts even recommend boiling water several times. It brings the taste-forming acids of the tea better to the development”, explains the expert.