Did you know that reboiling water is bad for your health?

What does ‘reboiling’ actually mean? It’s very simple. Reboiling water is when you boil it once, let it cool down and then boil it again. Most of us do it all the time without thinking. Doesn’t sound very dangerous, does it? However, some scientists believe that reboiling water is incredibly bad for your health. But why?

You put the kettle on to boil water and then forget about it. The hot water cools down, and then we boil the same water again. When we boil water, the chemistry of it changes, which is usually a good thing as it boils out volatile compounds and dissolves gases.

If you have perfectly pure distilled deionized water, nothing will happen if you reboil it once again, but ordinary tap water contains lots of different substances. When we boil it more than once, the chemical compounds in it change not for the best but for the worst.

Therefore, you’re actually concentrating many harmful chemicals instead of getting rid of them. If you boil the water too long or reboil it, you risk concentrating certain undesirable chemicals found in tap water.

Examples of chemicals that become more concentrated include nitrates, arsenic, and fluoride.


The World Health Organization (WHO) states that “Drinking-water poses the greatest threat to public health from arsenic. This, in turn, may lead to arsenic toxicity, which can develop physical effects slowly over a number of years, depending on the level of exposure. Dangers of arsenic toxicity include peripheral neuropathy, gastrointestinal symptoms, skin lesions, diabetes, renal systems effects, cardiovascular disease, and even cancer”.


Nitrates can naturally be found all around us: in the soil, water, and air. However, the chemicals become harmful when they are used as a food preservative, or when exposed to high heat – such as boiling water. When the nitrates are exposed to high temperatures, they turn into nitrosamines, which are carcinogenic.

Nitrates can be linked to many diseases such as leukemia, non-Hodkin lymphoma, cancers(including colon, bladder, ovarian, stomach, pancreatic, and esophageal cancer).


Fluoride has been studied by many scientists around the world. A lot of them believe that fluoride present in tap water could pose a serious threat to your health. However, despite the evidence of the dangerous effects of fluoride, it is still present in our water

The Harvard University took data from over 27 studies that were carried out within 22 years and linked fluoride exposure to neurological and cognitive function in children. The results were published in the Journal of Environment Health Sciences and concluded that fluoride found in drinking water resulted in lower IQ scored among children.

Moreover, everything that is dissolved in tap water that doesn’t easily evaporate when heated (called non-volatile substances) stays in the water no matter how long you boil it for. These substances will get more concentrated the longer you boil the water, as boiling concentrates whatever salts and impurities are present in the water.

No one can be absolutely sure of what exactly is present in our tap water. So, boiling your kettle more than once is not a great idea.

Besides, if you are a tea lover, reboiling water will affect the taste! When it comes to tea, its taste and color depend on the interaction between the two main components of tea – polyphenols, and caffeine. Each component is astringent on its own, but as a complex, the astringent character is reduced.

The acidity of water plays a critical role in the ionization of tea polyphenols and contributes to the stability of the above complex; therefore, twice-boiled water can easily spoil the taste of a nice cup of tea.


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This Post Has 2 Comments

  1. Hilary Waterland

    Eeek I’m guilty of that- off to empty and rinse kettle before my next cuppa!

  2. Pamela Cohen

    If you boil unfiltered water, yes it can concentrate the pollutants. In a covered teakettle, the gas can’t escape well or at all. A friend said the concentrated minerals might be a benefit, but better is hydrating with enough water. Maybe I will start boiling one time tea or coffee water in one of my many small saucepans. That means I cannot leave the room, as the water can boil down. When I was a kid, I melted my Mother’s good stainless large pan on the burner. No wonder I was left out of the will. Lol

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